Conversion of units

Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.

Techniques

See also: Dimensional analysis

Process overview

The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:

• The precision and accuracy of measurement and the associated uncertainty of measurement.
• The statistical confidence interval or tolerance interval of the initial measurement.
• The number of significant figures of the measurement.
• The intended use of the measurement including the engineering tolerances.
• Historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.

Some conversions from one system of units to another need to be exact, without increasing or decreasing the precision of the first measurement. This is sometimes called soft conversion. It does not involve changing the physical configuration of the item being measured.

By contrast, a hard conversion or an adaptive conversion may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system. It sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are sometimes allowed and used.

Conversion factors

A conversion factor is used to change the units of a measured quantity without changing its value. The unity bracket method of unit conversion[1] consists of a fraction in which the denominator is equal to the numerator, but they are in different units. Because of the identity property of multiplication, the value of a quantity will not change as long as it is multiplied by one.[2] Also, if the numerator and denominator of a fraction are equal to each other, then the fraction is equal to one. So as long as the numerator and denominator of the fraction are equivalent, they will not affect the value of the measured quantity.

The following example demonstrates how the unity bracket method[3] is used to convert the rate 5 kilometers per second to meters per second. The symbols km, m, and s represent kilometer, meter, and second, respectively.

${\displaystyle {\frac {5{\cancel {\text{km}}}}{\text{s}}}\cdot }$${\displaystyle {\frac {{1000}{\text{ m}}}{{1}{\cancel {\text{ km}}}}}}$${\displaystyle =}$${\displaystyle {\frac {5000\cdot {\text{m}}}{{\text{s}}\cdot {1}}}=}$${\displaystyle {\frac {5000{\text{ m}}}{\text{s}}}}$

Thus, it is found that 5 kilometers per second is equal to 5000 meters per second.

Software tools

There are many conversion tools. They are found in the function libraries of applications such as spreadsheets databases, in calculators, and in macro packages and plugins for many other applications such as the mathematical, scientific and technical applications.

There are many standalone applications that offer the thousands of the various units with conversions. For example, the free software movement offers a command line utility GNU units for Linux and Windows.

Calculation involving non-SI Units

In the cases where non-SI units are used, the numerical calculation of a formula can be done by first working out the pre-factor, and then plug in the numerical values of the given/known quantities.

For example, in the study of Bose–Einstein condensate[4], atomic mass m is usually given in daltons, instead of kilograms, and chemical potential μ is often given in Boltzmann constant times nanokelvin. The condensate's healing length is given by:

${\displaystyle \xi ={\frac {\hbar }{\sqrt {2m\mu }}}\,.}$

For a ²³Na condensate with chemical potential of (Boltzmann constant times) 128 nK, the calculation of healing length (in microns) can be done in two steps:

Calculate the pre-factor

Assume that ${\displaystyle m=1\,{\text{dalton}},\mu =1\,k_{B}\cdot {\text{nK}}\,,}$ this gives

${\displaystyle \xi ={\frac {\hbar }{\sqrt {2m\mu }}}=15.574\,\mu m\,,}$

which is our pre-factor.

Calculate the numbers

Now, make use of the fact that ${\displaystyle \xi \propto {\frac {1}{\sqrt {m\mu }}}}$. With ${\displaystyle m=23\,{\text{dalton}},\mu =128\,k_{B}\cdot {\text{nK}}}$, ${\displaystyle \xi ={\frac {15.574}{\sqrt {23*128}}}\,\mu m=0.287\,\mu m}$.

This method is especially useful for programming and/or making a worksheet, where input quantities are taking multiple different values; For example, with the pre-factor calculated above, it's very easy to see that the healing length of ¹⁷⁴Yb with chemical potential 20.3 nK is ${\displaystyle \xi ={\frac {15.574}{\sqrt {174*20.3}}}\,\mu m=0.262\,\mu m}$.

Tables of conversion factors

This article gives lists of conversion factors for each of a number of physical quantities, which are listed in the index. For each physical quantity, a number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10⁻⁶ metre). Within each table, the units are listed alphabetically, and the SI units (base or derived) are highlighted.

Legend

Symbol	Definition
≡	exactly equal
≈	approximately equal to
digits	indicates that digits repeat infinitely (e.g. 8.294369 corresponds to 8.294369369369369...)
(H)	of chiefly historical interest

Length

Length

Name of unit	Symbol	Definition	Relation to SI units
ångström	Å	≡ 1×10^−10 m	≡ 0.1 nm
astronomical unit	AU	≡ 149597870700 m ≈ Distance from Earth to Sun	≡ 149597870700 m [5]
attometre	am	≡ 1×10^−18 m	≡ 1×10^−18 m
barleycorn (H)		= ​^1⁄3 in (see note above about rounding)	≈ 8.46×10^−3 m
bohr, atomic unit of length	a0	= Bohr radius of hydrogen	≈ 5.2917721092(17)×10^−11 m[6]
cable length (imperial)		≡ 608 ft	≈ 185.3184 m
cable length (International)		≡ ​^1⁄10 nmi	≡ 185.2 m
cable length (US)		≡ 720 ft	= 219.456 m
chain (Gunter's; Surveyor's)	ch	≡ 66 ft (US) ≡ 4 rods [7]	≈ 20.11684 m
cubit (H)		≡ Distance from fingers to elbow ≈ 18 in	≈ 0.5 m
ell (H)	ell	≡ 45 in [8] (In England usually)	= 1.143 m
fathom	ftm	≡ 6 ft [8]	= 1.8288 m
femtometre	fm	≡ 1×10^−15 m	≡ 1×10^−15 m
fermi	fm	≡ 1×10^−15 m[8]	≡ 1×10^−15 m
finger		≡ ​^7⁄8 in	= 0.022225 m
finger (cloth)		≡ ​4 ^1⁄2 in	= 0.1143 m
foot (Benoît) (H)	ft (Ben)		≈ 0.304799735 m
foot (Cape) (H)		Legally defined as 1.033 English feet in 1859	≈ 0.314858 m
foot (Clarke's) (H)	ft (Cla)		≈ 0.3047972654 m
foot (Indian) (H)	ft Ind		≈ 0.304799514 m
foot, metric	mf	≡ 300 mm	≡ 0.3 m
foot, metric (Mesures usuelles) (H)		≡ ​^1⁄3 m	≡ 0.3 m
foot (International)	ft	≡ 0.3048 m ≡ ​^1⁄3 yd ≡ 12 inches	≡ 0.3048 m
foot (Sear's) (H)	ft (Sear)		≈ 0.30479947 m
foot (US Survey)	ft (US)	≡ ​^1200⁄3937 m [9]	≈ 0.304800610 m
french; charriere	F	≡ ​^1⁄3 mm	= 0.3 ×10^−3 m
furlong	fur	≡ 10 chains = 660 ft = 220 yd [8]	= 201.168 m
hand		≡ 4 in [8]	≡ 0.1016 m
inch (International)	in	≡ 2.54 cm ≡ ​^1⁄36 yd ≡ ​^1⁄12 ft	≡ 0.0254 m
league (land)	lea	≈ 1 hour walk, Currently defined in US as 3 Statute miles,[7] but historically varied from 2 to 9 km	≈ 4828 m
light-day		≡ 24 light-hours	≡ 2.59020683712×10^13 m
light-hour		≡ 60 light-minutes	≡ 1.0792528488×10^12 m
light-minute		≡ 60 light-seconds	≡ 1.798754748×10^10 m
light-second		≡ Distance light travels in one second in vacuum	≡ 299792458 m
light-year	ly	≡ Distance light travels in vacuum in 365.25 days [10]	≡ 9.4607304725808×10^15 m
line	ln	≡ ​^1⁄12 in [11]	= 0.002116 m
link (Gunter's; Surveyor's)	lnk	≡ ​^1⁄100 ch [8] ≡ 0.66 ft (US) ≡ 7.92 in	≈ 0.2011684 m
link (Ramsden's; Engineer's)	lnk	≡ 1 ft [8]	= 0.3048 m
metre (SI base unit) (meter)	m	≡ Distance light travels in ​^1⁄299792458 of a second in vacuum.[12] ≈ ​^1⁄10000000 of the distance from equator to pole.	≡ 1 m
mickey		≡ ​^1⁄200 in	= 1.27×10^−4 m
micrometre (old: micron)	μ; μm	≡ 1×10^−6 m	≡ 1×10^−6 m
mil; thou	mil	≡ 1×10^−3 in	≡ 2.54×10^−5 m
mil (Sweden and Norway)	mil	≡ 10 km	= 10000 m
mile (geographical) (H)		≡ 6082 ft	= 1853.7936 m
mile (international)	mi	≡ 80 chains ≡ 5280 ft ≡ 1760 yd	≡ 1609.344 m
mile (tactical or data)		≡ 6000 ft	≡ 1828.8 m
mile (telegraph) (H)	mi	≡ 6087 ft	= 1855.3176 m
mile (US Survey)	mi	≡ 5280 US Survey feet ≡ (5280 × ​^1200⁄3937) m	≈ 1609.347219 m
nail (cloth)		≡ ​2 ^1⁄4 in [8]	= 0.05715 m
nanometre	nm	≡ 1×10^−9 m	≡ 1×10^−9 m
nautical league	NL; nl	≡ 3 nmi [8]	= 5556 m
nautical mile (Admiralty)	NM (Adm); nmi (Adm)	= 6080 ft	= 1853.184 m
nautical mile (international)	NM; nmi	≡ 1852 m[13]	≡ 1852 m
nautical mile (US pre 1954)		≡ 1853.248 m	≡ 1853.248 m
pace		≡ 2.5 ft [8]	= 0.762 m
palm		≡ 3 in [8]	= 0.0762 m
parsec	pc	Distant point with a parallax shift of one arc second from a base of one astronomical unit. ≡ 648000/π AU[14][15]	≈ 30856775814913700 m[16]
pica		≡ 12 points	Dependent on point measures.
picometre	pm	≡ 1×10^−12 m	≡ 1×10^−12 m
point (American, English)[17][18]	pt	≡ ​^1⁄72.272 in	≈ 0.000351450 m
point (Didot; European) [18][19]	pt	≡ ​^1⁄12 × ​^1⁄72 of pied du roi; After 1878: ≡ ​^5⁄133 cm	≈ 0.00037597 m; After 1878: ≈ 0.00037593985 m
point (PostScript) [17]	pt	≡ ​^1⁄72 in	= 0.0003527 m
point (TeX) [17]	pt	≡ ​^1⁄72.27 in	= 0.0003514598 m
quarter		≡ ​^1⁄4 yd	= 0.2286 m
rod; pole; perch (H)	rd	≡ ​16 ^1⁄2 ft	= 5.0292 m
rope (H)	rope	≡ 20 ft [8]	= 6.096 m
shaku (Japan)		≡ 10/33 m	≈ 0.303 0303 m
span (H)		≡ 9 in [8]	= 0.2286 m
spat [20]			≡ 1×10^12 m
stick (H)		≡ 2 in	= 0.0508 m
toise (French, post 1667) (H)	T	≡ 27000/13853 m	≈ 1.949 0363 m
twip	twp	≡ ​^1⁄1440 in	= 1.7638×10^−5 m
x unit; siegbahn	xu		≈ 1.0021×10^−13 m [8]
yard (International)	yd	≡ 0.9144 m [9] ≡ 3 ft ≡ 36 in	≡ 0.9144 m
yoctometre	ym	≡ 1×10^−24 m	≡ 1×10^−24 m
zeptometre	zm	≡ 1×10^−21 m	≡ 1×10^−21 m

Area

Area

Name of unit	Symbol	Definition	Relation to SI units
acre (international)	ac	≡ 1 ch × 10 ch = 4840 sq yd	≡ 4046.8564224 m^2
acre (US survey)	ac	≡ 10 sq ch = 4840 sq yd, also 43560 sq ft	≈ 4046.873 m^2[21]
are	a	≡ 100 m^2	≡ 100 m^2
barn	b	≡ 10^−28 m^2	≡ 10^−28 m^2
barony		≡ 4000 ac	≡ 1.61874256896×10^7 m^2
board	bd	≡ 1 in × 1 ft	≡ 7.74192×10^−3 m^2
boiler horsepower equivalent direct radiation	bhp EDR	≡ 1 ft^2 × 1 bhp / (240 BTUIT/h)	≈ 12.958174 m^2
circular inch	circ in	≡ ​^π⁄4 sq in	≈ 5.067075×10^−4 m^2
circular mil; circular thou	circ mil	≡ ​^π⁄4 mil^2	≈ 5.067075×10^−10 m^2
cord		≡ 192 bd	≡ 1.48644864 m^2
cuerda (PR Survey)	cda	≡ 1 cda x 1 cda = 0.971222 acre	≡ 3930.395625 m^2
dunam		≡ 1000 m^2	= 1000 m^2
guntha (India)		≡ 121 sq yd	≈ 101.17 m^2
hectare	ha	≡ 10000 m^2	≡ 10000 m^2
hide		≈ 120 ac (variable)	≈ 5×10^5 m^2
rood	ro	≡ ​^1⁄4 ac	= 1011.7141056 m^2
ping		≡ ​^20⁄11 m × ​^20⁄11 m	≈ 3.306 m^2
section		≡ 1 mi × 1 mi	= 2.589988110336×10^6 m^2
shed		≡ 10^−52 m^2	= 10^−52 m^2
square (roofing)		≡ 10 ft × 10 ft	= 9.290304 m^2
square chain (international)	sq ch	≡ 66 ft × 66 ft = ​^1⁄10 ac	≡ 404.68564224 m^2
square chain (US Survey)	sq ch	≡ 66 ft (US) × 66 ft (US) = ​^1⁄10 US survey acre	≈ 404.6873 m^2
square foot	sq ft	≡ 1 ft × 1 ft	≡ 9.290304×10^−2 m^2
square foot (US Survey)	sq ft	≡ 1 ft (US) × 1 ft (US)	≈ 9.2903411613275×10^−2 m^2
square inch	sq in	≡ 1 in × 1 in	≡ 6.4516×10^−4 m^2
square kilometre	km^2	≡ 1 km × 1 km	= 10^6 m^2
square link (Gunter's)(International)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft	= 4.0468564224×10^−2 m^2
square link (Gunter's)(US Survey)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft (US) × 0.66 ft (US)	≈ 4.046872×10^−2 m^2
square link (Ramsden's)	sq lnk	≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft	= 0.09290304 m^2
square metre (SI unit)	m^2	≡ 1 m × 1 m	= 1 m^2
square mil; square thou	sq mil	≡ 1 mil × 1 mil	= 6.4516×10^−10 m^2
square mile	sq mi	≡ 1 mi × 1 mi	≡ 2.589988110336×10^6 m^2
square mile (US Survey)	sq mi	≡ 1 mi (US) × 1 mi (US)	≈ 2.58999847×10^6 m^2
square rod/pole/perch	sq rd	≡ 1 rd × 1 rd	= 25.29285264 m^2
square yard (International)	sq yd	≡ 1 yd × 1 yd	≡ 0.83612736 m^2
stremma		≡ 1000 m^2	= 1000 m^2
township		≡ 36 sq mi (US)	≈ 9.323994×10^7 m^2
yardland		≈ 30 ac	≈ 1.2×10^5 m^2

Volume

Volume

Name of unit	Symbol	Definition	Relation to SI units
acre-foot	ac ft	≡ 1 ac x 1 ft = 43560 cu ft	= 1233.48183754752 m^3
acre-inch		≡ 1 ac × 1 in	= 102.79015312896 m^3
barrel (imperial)	bl (imp)	≡ 36 gal (imp)	= 0.16365924 m^3
barrel (petroleum); archaic blue-barrel	bl; bbl	≡ 42 gal (US)	= 0.158987294928 m^3
barrel (US dry)	bl (US)	≡ 105 qt (US) = 105/32 bu (US lvl)	= 0.115628198985075 m^3
barrel (US fluid)	fl bl (US)	≡ ​31 ^1⁄2 gal (US)	= 0.119240471196 m^3
board-foot	fbm	≡ 144 cu in	≡ 2.359737216×10^−3 m^3
bucket (imperial)	bkt	≡ 4 gal (imp)	= 0.01818436 m^3
bushel (imperial)	bu (imp)	≡ 8 gal (imp)	= 0.03636872 m^3
bushel (US dry heaped)	bu (US)	≡ ​1 ^1⁄4 bu (US lvl)	= 0.0440488377086 m^3
bushel (US dry level)	bu (US lvl)	≡ 2150.42 cu in	= 0.03523907016688 m^3
butt, pipe		≡ 126 gal (US) (wine)	= 0.476961884784 m^3
coomb		≡ 4 bu (imp)	= 0.14547488 m^3
cord (firewood)		≡ 8 ft × 4 ft × 4 ft	= 3.624556363776 m^3
cord-foot		≡ 16 cu ft	= 0.453069545472 m^3
cubic fathom	cu fm	≡ 1 fm × 1 fm × 1 fm	= 6.116438863872 m^3
cubic foot	ft^3	≡ 1 ft × 1 ft × 1 ft	≡ 0.028316846592 m^3
cubic inch	in^3	≡ 1 in × 1 in × 1 in	≡ 16.387064×10^−6 m^3
cubic metre (SI unit)	m^3	≡ 1 m × 1 m × 1 m	≡ 1 m^3
cubic mile	cu mi	≡ 1 mi × 1 mi × 1 mi	≡ 4168181825.440579584 m^3
cubic yard	yd^3	≡ 27 cu ft	≡ 0.764554857984 m^3
cup (breakfast)		≡ 10 fl oz (imp)	= 284.130625×10^−6 m^3
cup (Canadian)	c (CA)	≡ 8 fl oz (imp)	= 227.3045×10^−6 m^3
cup (metric)	c	≡ 250.0×10^−6 m^3	= 250.0×10^−6 m^3
cup (US customary)	c (US)	≡ 8 US fl oz ≡ ​^1⁄16 gal (US)	= 236.5882365×10^−6 m^3
cup (US food nutrition labeling)	c (US)	≡ 240 mL[22]	= 2.4×10^−4 m^3
dash (imperial)		≡ ​^1⁄384 gi (imp) = ​^1⁄2 pinch (imp)	= 369.961751302083×10^−9 m^3
dash (US)		≡ ​^1⁄96 US fl oz = ​^1⁄2 US pinch	= 308.057599609375×10^−9 m^3
dessertspoon (imperial)		≡ ​^1⁄12 gi (imp)	= 11.8387760416×10^−6 m^3
drop (imperial)	gtt	≡ ​^1⁄288 fl oz (imp)	= 98.6564670138×10^−9 m^3
drop (imperial) (alt)	gtt	≡ ​^1⁄1824 gi (imp)	≈ 77.886684×10^−9 m^3
drop (medical)		≡ ​^0.9964⁄12 ml	= 83.03×10^−9 m^3
drop (medical)		≡ ​^1⁄12 ml	= 83.3×10^−9 m^3
drop (metric)		≡ ​^1⁄20 mL	= 50.0×10^−9 m^3
drop (US)	gtt	≡ ​^1⁄360 US fl oz	= 82.14869322916×10^−9 m^3
drop (US) (alt)	gtt	≡ ​^1⁄456 US fl oz	≈ 64.85423149671×10^−9 m^3
drop (US) (alt)	gtt	≡ ​^1⁄576 US fl oz	≈ 51.34293326823×10^−9 m^3
fifth		≡ ​^1⁄5 US gal	= 757.0823568×10^−6 m^3
firkin		≡ 9 gal (imp)	= 0.04091481 m^3
fluid drachm (imperial)	fl dr	≡ ​^1⁄8 fl oz (imp)	= 3.5516328125×10^−6 m^3
fluid dram (US); US fluidram	fl dr	≡ ​^1⁄8 US fl oz	= 3.6966911953125×10^−6 m^3
fluid scruple (imperial)	fl s	≡ ​^1⁄24 fl oz (imp)	= 1.18387760416×10^−6 m^3
gallon (beer)	beer gal	≡ 282 cu in	= 4.621152048×10^−3 m^3
gallon (imperial)	gal (imp)	≡ 4.54609 L	≡ 4.54609×10^−3 m^3
gallon (US dry)	gal (US)	≡ ​^1⁄8 bu (US lvl)	= 4.40488377086×10^−3 m^3
gallon (US fluid; Wine)	gal (US)	≡ 231 cu in	≡ 3.785411784×10^−3 m^3
gill (imperial); Noggin	gi (imp); nog	≡ 5 fl oz (imp)	= 142.0653125×10^−6 m^3
gill (US)	gi (US)	≡ 4 US fl oz	= 118.29411825×10^−6 m^3
hogshead (imperial)	hhd (imp)	≡ 2 bl (imp)	= 0.32731848 m^3
hogshead (US)	hhd (US)	≡ 2 fl bl (US)	= 0.238480942392 m^3
jigger (bartending)		≡ ​1 ^1⁄2 US fl oz	≈ 44.36×10^−6 m^3
kilderkin		≡ 18 gal (imp)	= 0.08182962 m^3
lambda	λ	≡ 1 mm^3	= 1×10^−9 m^3
last		≡ 80 bu (imp)	= 2.9094976 m^3
litre (liter)	L or l	≡ 1 dm^3 [23]	≡ 0.001 m^3
load		≡ 50 cu ft	= 1.4158423296 m^3
minim (imperial)	min	≡ ​^1⁄480 fl oz (imp) = 1/60 fl dr (imp)	= 59.1938802083×10^−9 m^3
minim (US)	min	≡ ​^1⁄480 US fl oz = ​^1⁄60 US fl dr	= 61.611519921875×10^−9 m^3
ounce (fluid imperial)	fl oz (imp)	≡ ​^1⁄160 gal (imp)	≡ 28.4130625×10^−6 m^3
ounce (fluid US customary)	US fl oz	≡ ​^1⁄128 gal (US)	≡ 29.5735295625×10^−6 m^3
ounce (fluid US food nutrition labeling)	US fl oz	≡ 30 mL[22]	≡ 3×10^−5 m^3
peck (imperial)	pk	≡ 2 gal (imp)	= 9.09218×10^−3 m^3
peck (US dry)	pk	≡ ​^1⁄4 US lvl bu	= 8.80976754172×10^−3 m^3
perch	per	≡ ​16 ^1⁄2 ft × ​1 ^1⁄2 ft × 1 ft	= 0.700841953152 m^3
pinch (imperial)		≡ ​^1⁄192 gi (imp) = 1/16 tsp (imp)	= 739.92350260416×10^−9 m^3
pinch (US)		≡ ​^1⁄48 US fl oz = 1/16 US tsp	= 616.11519921875×10^−9 m^3
pint (imperial)	pt (imp)	≡ ​^1⁄8 gal (imp)	= 568.26125×10^−6 m^3
pint (US dry)	pt (US dry)	≡ ​^1⁄64 bu (US lvl) ≡ ​^1⁄8 gal (US dry)	= 550.6104713575×10^−6 m^3
pint (US fluid)	pt (US fl)	≡ ​^1⁄8 gal (US)	= 473.176473×10^−6 m^3
pony		≡ ​^3⁄4 US fl oz	= 22.180147171875×10^−6 m^3
pottle; quartern		≡ ​^1⁄2 gal (imp) = 80 fl oz (imp)	= 2.273045×10^−3 m^3
quart (imperial)	qt (imp)	≡ ​^1⁄4 gal (imp)	= 1.1365225×10^−3 m^3
quart (US dry)	qt (US)	≡ ​^1⁄32 bu (US lvl) = ​^1⁄4 gal (US dry)	= 1.101220942715×10^−3 m^3
quart (US fluid)	qt (US)	≡ ​^1⁄4 gal (US fl)	= 946.352946×10^−6 m^3
quarter; pail		≡ 8 bu (imp)	= 0.29094976 m^3
register ton		≡ 100 cu ft	= 2.8316846592 m^3
sack (US)		≡ 3 bu (US lvl)	= 0.10571721050064 m^3
seam		≡ 8 bu [20]	= 0.29095 m^3
shot (US)		usually 1.5 US fl oz[20]	≈ 44.4×10^−6 m^3
strike (imperial)		≡ 2 bu (imp)	= 0.07273744 m^3
strike (US)		≡ 2 bu (US lvl)	= 0.07047814033376 m^3
tablespoon (Australian metric)			≡ 20.0×10^−6 m^3
tablespoon (Canadian)	tbsp	≡ ​^1⁄2 fl oz (imp)	= 14.20653125×10^−6 m^3
tablespoon (imperial)	tbsp	≡ ​^5⁄8 fl oz (imp)	= 17.7581640625×10^−6 m^3
tablespoon (metric)			≡ 15.0×10^−6 m^3
tablespoon (US customary)	tbsp	≡ ​^1⁄2 US fl oz	= 14.78676478125×10^−6 m^3
tablespoon (US food nutrition labeling)	tbsp	≡ 15 mL[22]	= 1.5×10^−5 m^3
teaspoon (Canadian)	tsp	≡ ​^1⁄6 fl oz (imp)	= 4.735510416×10^−6 m^3
teaspoon (imperial)	tsp	≡ ​^1⁄24 gi (imp)	= 5.91938802083×10^−6 m^3
teaspoon (metric)		≡ 5.0×10^−6 m^3	= 5.0×10^−6 m^3
teaspoon (US customary)	tsp	≡ ​^1⁄6 US fl oz	= 4.92892159375×10^−6 m^3
teaspoon (US food nutrition labeling)	tsp	≡ 5 mL[22]	= 5×10^−6 m^3
timber foot		≡ 1 cu ft	= 0.028316846592 m^3
ton (displacement)		≡ 35 cu ft	= 0.99108963072 m^3
ton (freight)		≡ 40 cu ft	= 1.13267386368 m^3
ton (water)		≡ 28 bu (imp)	= 1.01832416 m^3
tun		≡ 252 gal (wine)	= 0.953923769568 m^3
wey (US)		≡ 40 bu (US lvl)	= 1.4095628066752 m^3

Plane angle

Plane angle

Name of unit	Symbol	Definition	Relation to SI units
NATO mil	(various)	≡ ​^2π⁄6400 rad	≈ 0.981748×10^−3 rad
Swedish streck		≡ ​^2π⁄6300 rad	≈ 0.997302×10^−3 rad
milliradian	mrad	≡ ​^1⁄1000 rad	≈ 1×10^−3 rad
Warsaw Pact mil		≡ ​^2π⁄6000 rad	≈ 1.047167×10^−3 rad
arcminute; MOA	'	≡ ​^1°⁄60	≈ 0.290888×10^−3 rad
arcsecond	"	≡ ​^1°⁄3600	≈ 4.848137×10^−6 rad
centesimal minute of arc	'	≡ ​^1⁄100 grad	≈ 0.157080×10^−3 rad
centesimal second of arc	"	≡ ​^1⁄10000 grad	≈ 1.570796×10^−6 rad
degree (of arc)	°	≡ ​^1⁄360 of a revolution ≡ ​^π⁄180 rad	≈ 17.453293×10^−3 rad
grad; gradian; gon	grad	≡ ​^1⁄400 of a revolution ≡ ​^π⁄200 rad ≡ 0.9°	≈ 15.707963×10^−3 rad
octant		≡ 45°	≈ 0.785398 rad
quadrant		≡ 90°	≈ 1.570796 rad
radian (SI unit)	rad	The angle subtended at the center of a circle by an arc whose length is equal to the circle's radius. One full revolution encompasses 2π radians.	= 1 rad
sextant		≡ 60°	≈ 1.047198 rad
sign		≡ 30°	≈ 0.523599 rad

Solid angle

Solid angle

Name of unit	Symbol	Definition	Relation to SI units
spat		≡ 4π sr[20] – The solid angle subtended by a sphere at its centre.	≈ 12.56637 sr
square degree	deg^2; sq.deg.; (°)^2	≡ (​^π⁄180)^2 sr	≈ 0.30462×10^−3 sr
steradian (SI unit)	sr	The solid angle subtended at the center of a sphere of radius r by a portion of the surface of the sphere having an area r^2. A sphere subtends 4π sr.[20]	= 1 sr

Mass

Notes:

• See Weight for detail of mass/weight distinction and conversion.
• Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound.
• In this table, the unit gee is used to denote standard gravity in order to avoid confusion with the "g" symbol for grams.

Mass

Name of unit	Symbol	Definition	Relation to SI units
atomic mass unit, unified	u; AMU	Same as dalton (see below)	≈ 1.660539040(20)×10^−27 kg[7]
atomic unit of mass, electron rest mass	me		≈ 9.10938291(40)×10^−31 kg[24]
bag (coffee)		≡ 60 kg	= 60 kg
bag (Portland cement)		≡ 94 lb av	= 42.63768278 kg
barge		≡ ​22 ^1⁄2 short ton	= 20411.65665 kg
carat	kt	≡ ​3 ^1⁄6 gr	= 205.1965483 mg
carat (metric)	ct	≡ 200 mg	= 200 mg
clove		≡ 8 lb av	= 3.62873896 kg
crith		≡ mass of 1 L of hydrogen gas at STP	≈ 89.9349 mg
dalton	Da	1/12 the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest	≈ 1.660538921(73)×10^−27 kg[7]
dram (apothecary; troy)	dr t	≡ 60 gr	= 3.8879346 g
dram (avoirdupois)	dr av	≡ ​27 ^11⁄32 gr	= 1.7718451953125 g
electronvolt	eV	≡ 1 eV (energy unit) / c^2	= 1.78266184(45)×10^−36 kg[7]
gamma	γ	≡ 1 μg	= 1 μg
grain	gr	≡ ​^1⁄7000 lb av	≡ 64.79891 mg
grave	gv.	grave was the original name of the kilogram	≡ 1 kg
hundredweight (long)	long cwt or cwt	≡ 112 lb av	= 50.80234544 kg
hundredweight (short); cental	sh cwt	≡ 100 lb av	= 45.359237 kg
kilogram (kilogramme)	kg	≡ mass of the prototype near Paris ≈ mass of 1 litre of water	≡ 1 kg (SI base unit)[12]
kip	kip	≡ 1000 lb av	= 453.59237 kg
mark		≡ 8 oz t	= 248.8278144 g
mite		≡ ​^1⁄20 gr	= 3.2399455 mg
mite (metric)		≡ ​^1⁄20 g	= 50 mg
ounce (apothecary; troy)	oz t	≡ ​^1⁄12 lb t	= 31.1034768 g
ounce (avoirdupois)	oz av	≡ ​^1⁄16 lb	= 28.349523125 g
ounce (US food nutrition labelling)	oz	≡ 28 g[22]	= 28 g
pennyweight	dwt; pwt	≡ ​^1⁄20 oz t	= 1.55517384 g
point		≡ ​^1⁄100 ct	= 2 mg
pound (avoirdupois)	lb av	≡ 0.45359237 kg = 7000 grains	≡ 0.45359237 kg
pound (metric)		≡ 500 g	= 500 g
pound (troy)	lb t	≡ 5760 grains	= 0.3732417216 kg
quarter (imperial)		≡ ​^1⁄4 long cwt = 2 st = 28 lb av	= 12.70058636 kg
quarter (informal)		≡ ​^1⁄4 short ton	= 226.796185 kg
quarter, long (informal)		≡ ​^1⁄4 long ton	= 254.0117272 kg
quintal (metric)	q	≡ 100 kg	= 100 kg
scruple (apothecary)	s ap	≡ 20 gr	= 1.2959782 g
sheet		≡ ​^1⁄700 lb av	= 647.9891 mg
slug; geepound; hyl	slug	≡ 1 ɡ0 × 1 lb av × 1 s^2/ft	≈ 14.593903 kg
stone	st	≡ 14 lb av	= 6.35029318 kg
ton, assay (long)	AT	≡ 1 mg × 1 long ton ÷ 1 oz t	= 32.6 g
ton, assay (short)	AT	≡ 1 mg × 1 short ton ÷ 1 oz t	= 29.16 g
ton, long	long tn or ton	≡ 2240 lb	= 1016.0469088 kg
ton, short	sh tn	≡ 2000 lb	= 907.18474 kg
tonne (mts unit)	t	≡ 1000 kg	= 1000 kg
wey		≡ 252 lb = 18 st	= 114.30527724 kg (variants exist)
Zentner	Ztr.	Definitions vary.[20][25]

Density

Density

Name of unit	Symbol	Definition	Relation to SI units
gram per millilitre	g/mL	≡ g/mL	= 1000 kg/m^3
kilogram per cubic metre (SI unit)	kg/m^3	≡ kg/m^3	= 1 kg/m^3
kilogram per litre	kg/L	≡ kg/L	= 1000 kg/m^3
ounce (avoirdupois) per cubic foot	oz/ft^3	≡ oz/ft^3	≈ 1.001153961 kg/m^3
ounce (avoirdupois) per cubic inch	oz/in^3	≡ oz/in^3	≈ 1.729994044×10^3 kg/m^3
ounce (avoirdupois) per gallon (imperial)	oz/gal	≡ oz/gal	≈ 6.236023291 kg/m^3
ounce (avoirdupois) per gallon (US fluid)	oz/gal	≡ oz/gal	≈ 7.489151707 kg/m^3
pound (avoirdupois) per cubic foot	lb/ft^3	≡ lb/ft^3	≈ 16.01846337 kg/m^3
pound (avoirdupois) per cubic inch	lb/in^3	≡ lb/in^3	≈ 2.767990471×10^4 kg/m^3
pound (avoirdupois) per gallon (imperial)	lb/gal	≡ lb/gal	≈ 99.77637266 kg/m^3
pound (avoirdupois) per gallon (US fluid)	lb/gal	≡ lb/gal	≈ 119.8264273 kg/m^3
slug per cubic foot	slug/ft^3	≡ slug/ft^3	≈ 515.3788184 kg/m^3

Time

Time

Name of unit	Symbol	Definition	Relation to SI units
Atomic unit of time	au	≡ a0/(α⋅c)	≈ 2.418884254×10^−17 s
Callippic cycle		≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d	= 2.396736 Gs or 2.3983776 Gs[note 1]
Century	c	≡ 100 years (100 a)	= 3.1556952 Gs[note 2][note 3]
Day	d	= 24 h = 1440 min	= 86.4 ks[note 3]
Day (sidereal)	d	≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian (International Celestial Reference Frame)	≈ 86.1641 ks
Decade	dec	≡ 10 years (10 a)	= 315.569520 Ms[note 2][note 3]
Fortnight	fn	≡ 2 wk	= 1.2096 Ms[note 3]
Helek		≡ ​^1⁄1080 h	= 3.3 s
Hipparchic cycle		≡ 4 Callippic cycles - 1 d	= 9.593424 Gs
Hour	h	≡ 60 min	= 3.6 ks[note 3]
Jiffy	j	≡ ​^1⁄60 s	= 16.6 ms
Jiffy (alternative)	ja	≡ ​^1⁄100 s	= 10 ms
Ke (quarter of an hour)		≡ ​^1⁄4 h = ​^1⁄96 d = 15 min	= 900 s
Ke (traditional)		≡ ​^1⁄100 d = 14.4 min	= 864 s
Lustre; Lustrum		≡ 5 a of 365 d[note 4]	= 157.68 Ms
Metonic cycle; enneadecaeteris		≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a	= 599.616 Ms
Millennium		≡ 1000 years (1000 a)	= 31.556952 Gs[note 2][note 3]
Milliday	md	≡ ​^1⁄1000 d	= 86.4 s
Minute	min	≡ 60 s, due to leap seconds sometimes 59 s or 61 s,	= 60 s[note 3]
Moment		≡ 90 s	= 90 s
Month (full)	mo	≡ 30 d[26]	= 2.592×10^6 s[note 3]
Month (Greg. av.)	mo	= 30.436875 d	≈ 2.6297 Ms[note 3]
Month (hollow)	mo	≡ 29 d[26]	= 2.5056 Ms[note 3]
Month (synodic)	mo	Cycle time of moon phases ≈ 29.530589 d (average)	≈ 2.551 Ms
Octaeteris		= 48 mo (full) + 48 mo (hollow) + 3 mo (full)[27][28] = 8 a of 365.25 d = 2922 d	= 252.4608 Ms[note 3]
Planck time		≡ (​^Gℏ⁄c^5)^​1⁄2	≈ 5.39116×10^−44 s[29]
Second	s	Time of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at 0 K[12] (but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of 299792458 metres.	(SI base unit)
Shake		≡ 10^−8 s	= 10 ns
Sigma		≡ 10^−6 s	= 1 μs
Sothic cycle		≡ 1461 a of 365 d	= 46.074096 Gs
Svedberg	S	≡ 10^−13 s	= 100 fs
Week	wk	≡ 7 d = 168 h = 10080 min	= 604.8 ks[note 3]
Year (common)	a, y, or yr	365 d	= 31.536 Ms[note 3][note 3][30]
Year (Gregorian)	a, y, or yr	= 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See leap year for details.	= 31.556952 Ms[note 3]
Year (Julian)	a, y, or yr	= 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years	= 31.5576 Ms
Year (leap)	a, y, or yr	366 d	= 31.6224 Ms[note 3][30]
Year (mean tropical)	a, y, or yr	Conceptually, the length of time it takes for the Sun to return to the same position in the cycle of seasons, [Converter 1] approximately 365.24219 d, each day being 86400 SI seconds[31]	≈ 31.556925 Ms
Year (sidereal)	a, y, or yr	≡ Time taken for Sun to return to the same position with respect to the stars of the celestial sphere, approximately 365.256363 d	≈ 31.5581497632 Ms
Notes: see Callippic cycle for explanation of the differences This is based on the average Gregorian year. See above for definition of year lengths. Where UTC is observed, the length of this unit may increase or decrease depending on the number of leap seconds which occur during the time interval in question. The length of ancient lustral cycles was not constant; see Lustrum for more details

Frequency

Frequency

Name of unit	Symbol	Definition	Relation to SI units
Actions per minute	APM	≡ 1/60 Hz	≈ 0.0167 Hz
Cycle per second	cps	≡ 1 Hz	= 1 cps = 1 Hz
degree per second	deg/s	≡ 1 °/s ≡ 1/360 Hz	= 0.0027 Hz
hertz (SI unit)	Hz	≡ One cycle per second	= 1 Hz = 1/s
Radian per second	rad/s	≡ 1/(2π) Hz	≈ 0.159155 Hz
revolutions per minute	rpm	≡ One unit rpm equals one rotation completed around a fixed axis in one minute of time.	≈ 0.104719755 rad/s

Speed or velocity

Speed

Name of unit	Symbol	Definition	Relation to SI units
foot per hour	fph	≡ 1 ft/h	= 8.46×10^−5 m/s
foot per minute	fpm	≡ 1 ft/min	= 5.08×10^−3 m/s
foot per second	fps	≡ 1 ft/s	= 3.048×10^−1 m/s
furlong per fortnight		≡ furlong/fortnight	≈ 1.663095×10^−4 m/s
inch per hour	iph	≡ 1 in/h	= 7.05×10^−6 m/s
inch per minute	ipm	≡ 1 in/min	= 4.23×10^−4 m/s
inch per second	ips	≡ 1 in/s	= 2.54×10^−2 m/s
kilometre per hour	km/h	≡ 1 km/h	= 2.7×10^−1 m/s
knot	kn	≡ 1 nmi/h = 1.852 km/h	= 0.514 m/s
knot (Admiralty)	kn	≡ 1 NM (Adm)/h = 1.853184 km/h	= 0.514773 m/s
mach number	M	Ratio of the speed to the speed of sound[note 1] in the medium (unitless).	≈ 340 m/s in air at sea level ≈ 295 m/s in air at jet altitudes
metre per second (SI unit)	m/s	≡ 1 m/s	= 1 m/s
mile per hour	mph	≡ 1 mi/h	= 0.44704 m/s
mile per minute	mpm	≡ 1 mi/min	= 26.8224 m/s
mile per second	mps	≡ 1 mi/s	= 1609.344 m/s
speed of light in vacuum	c	≡ 299792458 m/s	= 299792458 m/s
speed of sound in air	s	1225 to 1062 km/h (761–660 mph or 661–574 kn)[note 1]	≈ 340 to 295 m/s
Note The speed of sound varies especially with temperature and pressure from about 340 m/s (1,225 km/h or 761 mph or 661 kn) in air at sea level to about 300 m/s (1,062 km/h or 660 mph or 573 kn) at jet altitudes (12200 m or 40000 ft).[32]

A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

Flow (volume)

Flow

Name of unit	Symbol	Definition	Relation to SI units
cubic foot per minute	CFM	≡ 1 ft^3/min	= 4.719474432×10^−4 m^3/s
cubic foot per second	ft^3/s	≡ 1 ft^3/s	= 0.028316846592 m^3/s
cubic inch per minute	in^3/min	≡ 1 in^3/min	= 2.7311773×10^−7 m^3/s
cubic inch per second	in^3/s	≡ 1 in^3/s	= 1.6387064×10^−5 m^3/s
cubic metre per second (SI unit)	m^3/s	≡ 1 m^3/s	= 1 m^3/s
gallon (US fluid) per day	GPD	≡ 1 gal/d	= 4.381263638×10^−8 m^3/s
gallon (US fluid) per hour	GPH	≡ 1 gal/h	= 1.051503273×10^−6 m^3/s
gallon (US fluid) per minute	GPM	≡ 1 gal/min	= 6.30901964×10^−5 m^3/s
litre per minute	l/min or L/min	≡ 1 L/min	= 1.6×10^−5 m^3/s

Acceleration

Acceleration

Name of unit	Symbol	Definition	Relation to SI units
foot per hour per second	fph/s	≡ 1 ft/(h⋅s)	= 8.46×10^−5 m/s^2
foot per minute per second	fpm/s	≡ 1 ft/(min⋅s)	= 5.08×10^−3 m/s^2
foot per second squared	fps^2	≡ 1 ft/s^2	= 3.048×10^−1 m/s^2
gal; galileo	Gal	≡ 1 cm/s^2	= 10^−2 m/s^2
inch per minute per second	ipm/s	≡ 1 in/(min⋅s)	= 4.23×10^−4 m/s^2
inch per second squared	ips^2	≡ 1 in/s^2	= 2.54×10^−2 m/s^2
knot per second	kn/s	≡ 1 kn/s	≈ 5.14×10^−1 m/s^2
metre per second squared (SI unit)	m/s^2	≡ 1 m/s^2	= 1 m/s^2
mile per hour per second	mph/s	≡ 1 mi/(h⋅s)	= 4.4704×10^−1 m/s^2
mile per minute per second	mpm/s	≡ 1 mi/(min⋅s)	= 26.8224 m/s^2
mile per second squared	mps^2	≡ 1 mi/s^2	= 1.609344×10^3 m/s^2
standard gravity	ɡ0	≡ 9.80665 m/s^2	= 9.80665 m/s^2

Force

Force

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of force		≡ ​^me⋅α2⋅c2⁄a0	≈ 8.23872206×10^−8 N[33]
dyne (cgs unit)	dyn	≡ g⋅cm/s^2	= 10^−5 N
kilogram-force; kilopond; grave-force	kgf; kp; Gf	≡ ɡ0 × 1 kg	= 9.80665 N
kip; kip-force	kip; kipf; klbf	≡ ɡ0 × 1000 lb	= 4.4482216152605×10^3 N
milligrave-force, gravet-force	mGf; gf	≡ ɡ0 × 1 g	= 9.80665 mN
long ton-force	tnf	≡ ɡ0 × 1 long ton	= 9.96401641818352×10^3 N
newton (SI unit)	N	A force capable of giving a mass of one kilogram an acceleration of one metre per second per second.[34]	= 1 N = 1 kg⋅m/s^2
ounce-force	ozf	≡ ɡ0 × 1 oz	= 0.27801385095378125 N
pound-force	lbf	≡ ɡ0 × 1 lb	= 4.4482216152605 N
poundal	pdl	≡ 1 lb⋅ft/s^2	= 0.138254954376 N
short ton-force	tnf	≡ ɡ0 × 1 short ton	= 8.896443230521×10^3 N
sthene (mts unit)	sn	≡ 1 t⋅m/s^2	= 10^3 N

See also: Conversion between weight (force) and mass

Pressure or mechanical stress

Pressure

Name of unit	Symbol	Definition	Relation to SI units
atmosphere (standard)	atm		≡ 101325 Pa[35]
atmosphere (technical)	at	≡ 1 kgf/cm^2	= 9.80665×10^4 Pa[35]
bar	bar	≡ 100000 Pa	≡ 10^5 Pa
barye (cgs unit)		≡ 1 dyn/cm^2	= 0.1 Pa
centimetre of mercury	cmHg	≡ 13595.1 kg/m^3 × 1 cm × ɡ0	≈ 1.33322×10^3 Pa[35]
centimetre of water (4 °C)	cmH2O	≈ 999.972 kg/m^3 × 1 cm × ɡ0	≈ 98.0638 Pa[35]
foot of mercury (conventional)	ftHg	≡ 13595.1 kg/m^3 × 1 ft × ɡ0	≈ 4.063666×10^4 Pa[35]
foot of water (39.2 °F)	ftH2O	≈ 999.972 kg/m^3 × 1 ft × ɡ0	≈ 2.98898×10^3 Pa[35]
inch of mercury (conventional)	inHg	≡ 13595.1 kg/m^3 × 1 in × ɡ0	≈ 3.386389×10^3 Pa[35]
inch of water (39.2 °F)	inH2O	≈ 999.972 kg/m^3 × 1 in × ɡ0	≈ 249.082 Pa[35]
kilogram-force per square millimetre	kgf/mm^2	≡ 1 kgf/mm^2	= 9.80665×10^6 Pa[35]
kip per square inch	ksi	≡ 1 kipf/sq in	≈ 6.894757×10^6 Pa[35]
long ton per square foot		≡ 1 long ton × ɡ0 / 1 sq ft	≈ 1.0725178011595×10^5 Pa
micrometre of mercury	μmHg	≡ 13595.1 kg/m^3 × 1 μm × ɡ0 ≈ 0.001 torr	≈ 0.1333224 Pa[35]
millimetre of mercury	mmHg	≡ 13595.1 kg/m^3 × 1 mm × ɡ0 ≈ 1 torr	≈ 133.3224 Pa[35]
millimetre of water (3.98 °C)	mmH2O	≈ 999.972 kg/m^3 × 1 mm × ɡ0 = 0.999972 kgf/m^2	= 9.80638 Pa
pascal (SI unit)	Pa	≡ N/m^2 = kg/(m⋅s^2)	= 1 Pa[36]
pièze (mts unit)	pz	≡ 1000 kg/m⋅s^2	= 10^3 Pa = 1 kPa
pound per square foot	psf	≡ 1 lbf/ft^2	≈ 47.88026 Pa[35]
pound per square inch	psi	≡ 1 lbf/in^2	≈ 6.894757×10^3 Pa[35]
poundal per square foot	pdl/sq ft	≡ 1 pdl/sq ft	≈ 1.488164 Pa[35]
short ton per square foot		≡ 1 short ton × ɡ0 / 1 sq ft	≈ 9.5760518×10^4 Pa
torr	torr	≡ ​^101325⁄760 Pa	≈ 133.3224 Pa[35]

Torque or moment of force

Torque

Name of unit	Symbol	Definition	Relation to SI units
pound-force-foot	lbf•ft	≡ ɡ0 × 1 lb × 1 ft	= 1.3558179483314004 N⋅m
poundal-ft	pdl•ft	≡ 1 lb⋅ft^2/s^2	= 4.21401100938048×10^−2 N⋅m
pound force-inch	lbf•in	≡ ɡ0 × 1 lb × 1 in	= 0.1129848290276167 N⋅m
kilogram force-meter	kgf•m	≡ ɡ0 × N × m	= 9.80665 N⋅m
Newton metre (SI unit)	N⋅m	≡ N × m = kg⋅m^2/s^2	= 1 N⋅m

Energy

Energy

Name of unit	Symbol	Definition	Relation to SI units
barrel of oil equivalent	boe	≈ 5.8×10^6 BTU59 °F	≈ 6.12×10^9 J
British thermal unit (ISO)	BTUISO	≡ 1.0545×10^3 J	= 1.0545×10^3 J
British thermal unit (International Table)	BTUIT		= 1.05505585262×10^3 J
British thermal unit (mean)	BTUmean		≈ 1.05587×10^3 J
British thermal unit (thermochemical)	BTUth		≈ 1.054350×10^3 J
British thermal unit (39 °F)	BTU39 °F		≈ 1.05967×10^3 J
British thermal unit (59 °F)	BTU59 °F	≡ 1.054804×10^3 J	= 1.054804×10^3 J
British thermal unit (60 °F)	BTU60 °F		≈ 1.05468×10^3 J
British thermal unit (63 °F)	BTU63 °F		≈ 1.0546×10^3 J
calorie (International Table)	calIT	≡ 4.1868 J	= 4.1868 J
calorie (mean)	calmean	​^1⁄100 of the energy required to warm one gram of air-free water from 0 °C to 100 °C at a pressure of 1 atm	≈ 4.19002 J
calorie (thermochemical)	calth	≡ 4.184 J	= 4.184 J
Calorie (US; FDA)	Cal	≡ 1 kcal = 1000 cal	= 4184 J
calorie (3.98 °C)	cal3.98 °C		≈ 4.2045 J
calorie (15 °C)	cal15 °C	≡ 4.1855 J	= 4.1855 J
calorie (20 °C)	cal20 °C		≈ 4.1819 J
Celsius heat unit (International Table)	CHUIT	≡ 1 BTUIT × 1 K/°R	= 1.899100534716×10^3 J
cubic centimetre of atmosphere; standard cubic centimetre	cc atm; scc	≡ 1 atm × 1 cm^3	= 0.101325 J
cubic foot of atmosphere; standard cubic foot	cu ft atm; scf	≡ 1 atm × 1 ft^3	= 2.8692044809344×10^3 J
cubic foot of natural gas		≡ 1000 BTUIT	= 1.05505585262×10^6 J
cubic yard of atmosphere; standard cubic yard	cu yd atm; scy	≡ 1 atm × 1 yd^3	= 77.4685209852288×10^3 J
electronvolt	eV	≡ e × 1 V	≈ 1.602176565(35)×10^−19 J
erg (cgs unit)	erg	≡ 1 g⋅cm^2/s^2	= 10^−7 J
foot-pound force	ft lbf	≡ ɡ0 × 1 lb × 1 ft	= 1.3558179483314004 J
foot-poundal	ft pdl	≡ 1 lb⋅ft^2/s^2	= 4.21401100938048×10^−2 J
gallon-atmosphere (imperial)	imp gal atm	≡ 1 atm × 1 gal (imp)	= 460.63256925 J
gallon-atmosphere (US)	US gal atm	≡ 1 atm × 1 gal (US)	= 383.5568490138 J
hartree, atomic unit of energy	Eh	≡ me⋅α^2⋅c^2 (= 2 Ry)	≈ 4.359744×10^−18 J
horsepower-hour	hp⋅h	≡ 1 hp × 1 h	= 2.684519537696172792×10^6 J
inch-pound force	in lbf	≡ ɡ0 × 1 lb × 1 in	= 0.1129848290276167 J
joule (SI unit)	J	The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force.[34]	= 1 J = 1 m⋅N = 1 kg⋅m^2/s^2 = 1 C⋅V = 1 W⋅s
kilocalorie; large calorie	kcal; Cal	≡ 1000 calIT	= 4.1868×10^3 J
kilowatt-hour; Board of Trade Unit	kW⋅h; B.O.T.U.	≡ 1 kW × 1 h	= 3.6×10^6 J
litre-atmosphere	l atm; sl	≡ 1 atm × 1 L	= 101.325 J
quad		≡ 10^15 BTUIT	= 1.05505585262×10^18 J
rydberg	Ry	≡ R∞⋅ℎ⋅c	≈ 2.179872×10^−18 J
therm (E.C.)		≡ 100000 BTUIT	= 105.505585262×10^6 J
therm (US)		≡ 100000 BTU59 °F	= 105.4804×10^6 J
thermie	th	≡ 1 McalIT	= 4.1868×10^6 J
tonne of coal equivalent	TCE	≡ 7 Gcalth	= 29.288×10^9 J
tonne of oil equivalent	toe	≡ 10 GcalIT	= 41.868×10^9 J
ton of TNT	tTNT	≡ 1 Gcalth	= 4.184×10^9 J
watt hour	W⋅h	≡ 1 W × 1 h	= 3.6×10^3 J
watt second	W⋅s	≡ 1 J	= 1×10^0 J

Power or heat flow rate

Power

Name of unit	Symbol	Definition	Relation to SI units
atmosphere-cubic centimetre per minute	atm ccm	≡ 1 atm × 1 cm^3/min	= 1.68875×10^−3 W
atmosphere-cubic centimetre per second	atm ccs	≡ 1 atm × 1 cm^3/s	= 0.101325 W
atmosphere-cubic foot per hour	atm cfh	≡ 1 atm × 1 cu ft/h	= 0.79700124704 W
atmosphere-cubic foot per minute	atm cfm	≡ 1 atm × 1 cu ft/min	= 47.82007468224 W
atmosphere-cubic foot per second	atm cfs	≡ 1 atm × 1 cu ft/s	= 2.8692044809344×10^3 W
BTU (International Table) per hour	BTUIT/h	≡ 1 BTUIT/h	≈ 0.293071 W
BTU (International Table) per minute	BTUIT/min	≡ 1 BTUIT/min	≈ 17.584264 W
BTU (International Table) per second	BTUIT/s	≡ 1 BTUIT/s	= 1.05505585262×10^3 W
calorie (International Table) per second	calIT/s	≡ 1 calIT/s	= 4.1868 W
erg per second	erg/s	≡ 1 erg/s	= 10^−7 W
foot-pound-force per hour	ft⋅lbf/h	≡ 1 ft lbf/h	≈ 3.766161×10^−4 W
foot-pound-force per minute	ft⋅lbf/min	≡ 1 ft lbf/min	= 2.259696580552334×10^−2 W
foot-pound-force per second	ft⋅lbf/s	≡ 1 ft lbf/s	= 1.3558179483314004 W
horsepower (boiler)	hp	≈ 34.5 lb/h × 970.3 BTUIT/lb	≈ 9809.5 W[37]
horsepower (European electrical)	hp	≡ 75 kp⋅m/s	= 736 W
horsepower (electrical)	hp	≡ 746 W	= 746 W[37]
horsepower (mechanical)	hp	≡ 550 ft⋅lbf/s[37]	= 745.69987158227022 W
horsepower (metric)	hp or PS	≡ 75 m⋅kgf/s	= 735.49875 W[37]
litre-atmosphere per minute	L·atm/min	≡ 1 atm × 1 L/min	= 1.68875 W
litre-atmosphere per second	L·atm/s	≡ 1 atm × 1 L/s	= 101.325 W
lusec	lusec	≡ 1 L·µmHg/s [20]	≈ 1.333×10^−4 W
poncelet	p	≡ 100 m⋅kgf/s	= 980.665 W
square foot equivalent direct radiation	sq ft EDR	≡ 240 BTUIT/h	≈ 70.337057 W
ton of air conditioning		≡ 2000 lb of ice melted / 24 h	≈ 3504 W
ton of refrigeration (imperial)		≡ 2240 lb × iceIT / 24 h: iceIT = 144 °F × 2326 J/kg⋅°F	≈ 3.938875×10^3 W
ton of refrigeration (IT)		≡ 2000 lb × iceIT / 24 h: iceIT = 144 °F × 2326 J/kg⋅°F	≈ 3.516853×10^3 W
watt (SI unit)	W	The power which in one second of time gives rise to one joule of energy.[34]	= 1 W = 1 J/s = 1 N⋅m/s = 1 kg⋅m^2/s^3

Action

Action

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of action	au	≡ ℏ ≡ ​^ℎ⁄2π	≈ 1.05457168×10^−34 J⋅s[38]

Dynamic viscosity

Dynamic viscosity

Name of unit	Symbol	Definition	Relation to SI units
pascal second (SI unit)	Pa⋅s	≡ N⋅s/m^2, kg/(m⋅s)	= 1 Pa⋅s
poise (cgs unit)	P	≡ 1 barye⋅s	= 0.1 Pa⋅s
pound per foot hour	lb/(ft⋅h)	≡ 1 lb/(ft⋅h)	≈ 4.133789×10^−4 Pa⋅s
pound per foot second	lb/(ft⋅s)	≡ 1 lb/(ft⋅s)	≈ 1.488164 Pa⋅s
pound-force second per square foot	lbf⋅s/ft^2	≡ 1 lbf⋅s/ft^2	≈ 47.88026 Pa⋅s
pound-force second per square inch	lbf⋅s/in^2	≡ 1 lbf⋅s/in^2	≈ 6894.757 Pa⋅s

Kinematic viscosity

Kinematic viscosity

Name of unit	Symbol	Definition	Relation to SI units
square foot per second	ft^2/s	≡ 1 ft^2/s	= 0.09290304 m^2/s
square metre per second (SI unit)	m^2/s	≡ 1 m^2/s	= 1 m^2/s
stokes (cgs unit)	St	≡ 1 cm^2/s	= 10^−4 m^2/s

Electric current

Electric current

Name of unit	Symbol	Definition	Relation to SI units
ampere (SI base unit)	A	≡ The constant current needed to produce a force of 2 ×10^−7 newton per metre between two straight parallel conductors of infinite length and negligible circular cross-section placed one metre apart in a vacuum.[12]	= 1 A = 1 C/s
electromagnetic unit; abampere (cgs unit)	abamp	≡ 10 A	= 10 A
esu per second; statampere (cgs unit)	esu/s	≡ ​^0.1 A⋅m/s⁄c	≈ 3.335641×10^−10 A

Electric charge

Electric charge

Name of unit	Symbol	Definition	Relation to SI units
abcoulomb; electromagnetic unit (cgs unit)	abC; emu	≡ 10 C	= 10 C
atomic unit of charge	au	≡ e	≈ 1.602176462×10^−19 C
coulomb	C	≡ The amount of electricity carried in one second of time by one ampere of current.[34]	= 1 C = 1 A⋅s
faraday	F	≡ 1 mol × NA⋅e	≈ 96485.3383 C
milliampere hour	mA⋅h	≡ 0.001 A × 1 h	= 3.6 C
statcoulomb; franklin; electrostatic unit (cgs unit)	statC; Fr; esu	≡ ​^0.1 A⋅m⁄c	≈ 3.335641×10^−10 C

Electric dipole

Electric dipole

Name of unit	Symbol	Definition	Relation to SI units
atomic unit of electric dipole moment	ea0		≈ 8.47835281×10^−30 C⋅m[39]
coulomb meter	C⋅m		= 1 C × 1 m
debye	D	= 10^−10 esu⋅Å	= 3.33564095×10^−30 C⋅m[40]

Electromotive force, electric potential difference

Voltage, electromotive force

Name of unit	Symbol	Definition	Relation to SI units
abvolt (cgs unit)	abV	≡ 10^−8 V	= 10^−8 V
statvolt (cgs unit)	statV	≡ c⋅(1 μJ/A⋅m)	= 299.792458 V
volt (SI unit)	V	The difference in electric potential across two points along a conducting wire carrying one ampere of constant current when the power dissipated between the points equals one watt.[34]	= 1 V = 1 W/A = 1 kg⋅m^2/(A⋅s^3) = 1 J/C

Electrical resistance

Electrical resistance

Name of unit	Symbol	Definition	Relation to SI units
ohm (SI unit)	Ω	The resistance between two points in a conductor when one volt of electric potential difference, applied to these points, produces one ampere of current in the conductor.[34]	= 1 Ω = 1 V/A = 1 kg⋅m^2/(A^2⋅s^3)

Capacitance

Capacitor's ability to store charge

Name of unit	Symbol	Definition	Relation to SI units
farad (SI unit)	F	The capacitance between two parallel plates that results in one volt of potential difference when charged by one coulomb of electricity.[34]	= 1 F = 1 C/V = 1 A^2⋅s^4/(kg⋅m^2)

Magnetic flux

magnetic flux

Name of unit	Symbol	Definition	Relation to SI units
maxwell (CGS unit)	Mx	≡ 10^−8 Wb[37]	= 10^−8 Wb
weber (SI unit)	Wb	Magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.[34]	= 1 Wb = 1 V⋅s = 1 kg⋅m^2/(A⋅s^2)

Magnetic flux density

What physicists call Magnetic field is called Magnetic flux density by electrical engineers and magnetic induction by applied mathematicians and electrical engineers.

Name of unit	Symbol	Definition	Relation to SI units
gauss (CGS unit)	G	≡ Mx/cm^2 = 10^−4 T	= 10^−4 T [41]
tesla (SI unit)	T	≡ Wb/m^2	= 1 T = 1 Wb/m^2 = 1 kg/(A⋅s^2)

Inductance

Inductance

Name of unit	Symbol	Definition	Relation to SI units
henry (SI unit)	H	The inductance of a closed circuit that produces one volt of electromotive force when the current in the circuit varies at a uniform rate of one ampere per second.[34]	= 1 H = 1 Wb/A = 1 kg⋅m^2/(A⋅s)^2

Temperature

Further information: Conversion of units of temperature

Temperature

Name of unit	Symbol	Definition	Relation to SI units
degree Celsius	°C	[°C] ≡ [K] − 273.15	[K] ≡ [°C] + 273.15
degree Delisle	°De		[K] = 373.15 − [°De] × ​^2⁄3
degree Fahrenheit	°F	[°F] ≡ [°C] × ​^9⁄5 + 32	[K] ≡ ([°F] + 459.67) × ​^5⁄9
degree Newton	°N		[K] = [°N] × ​^100⁄33 + 273.15
degree Rankine	°R;	[°R] ≡ [K] × ​^9⁄5	[K] ≡ [°R] × 5/9
degree Réaumur	°Ré		[K] = [°Ré] × ​^5⁄4 + 273.15
degree Rømer	°Rø		[K] = ([°Rø] − 7.5) × ​^40⁄21 + 273.15
Regulo Gas Mark	GM	[°F] ≡ [GM] × 25 + 300	[K] ≡ [GM] × ​^125⁄9 + 422.038
kelvin (SI base unit)	K	≡ ​^1⁄273.16 of the thermodynamic temperature of the triple point of water.[12]	≡ 1 K

Information entropy

Information entropy

Name of unit	Symbol	Definition	Relation to SI units	Relation to bits
natural unit of information; nip; nepit	nat
shannon; bit	Sh; bit; b	≡ ln(2) × nat	≈ 0.693147 nat	= 1 bit
hartley; ban	Hart; ban	≡ ln(10) × nat	≈ 2.302585 nat
nibble		≡ 4 bits		= 2^2 bit
byte	B	≡ 8 bits		= 2^3 bit
kilobyte (decimal)	kB	≡ 1000 B		= 8000 bit
kilobyte (kibibyte)	KB; KiB	≡ 1024 B		= 2^13 bit = 8192 bit

Modern standards (such as ISO 80000) prefer the shannon to the bit as a unit for a quantity of information entropy, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning.

Luminous intensity

The candela is the preferred nomenclature for the SI unit.

Luminous intensity

Name of unit	Symbol	Definition	Relation to SI units
candela (SI base unit); candle	cd	The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.[12]	= 1 cd
candlepower (new)	cp	≡ cd The use of candlepower as a unit is discouraged due to its ambiguity.	= 1 cd
candlepower (old, pre-1948)	cp	Varies and is poorly reproducible.[42] Approximately 0.981 cd.[20]	≈ 0.981 cd

Luminance

Luminance

Name of unit	Symbol	Definition	Relation to SI units
candela per square foot	cd/ft^2	≡ cd/ft^2	≈ 10.763910417 cd/m^2
candela per square inch	cd/in^2	≡ cd/in^2	≈ 1550.0031 cd/m^2
candela per square metre (SI unit); nit (deprecated[20])	cd/m^2	≡ cd/m^2	= 1 cd/m^2
footlambert	fL	≡ (1/π) cd/ft^2	≈ 3.4262590996 cd/m^2
lambert	L	≡ (10^4/π) cd/m^2	≈ 3183.0988618 cd/m^2
stilb (CGS unit)	sb	≡ 10^4 cd/m^2	= 10^4 cd/m^2

Luminous flux

Luminous flux

Name of unit	Symbol	Definition	Relation to SI units
lumen (SI unit)	lm	≡ cd⋅sr	= 1 lm = 1 cd⋅sr

Illuminance

Illuminance

Name of unit	Symbol	Definition	Relation to SI units
footcandle; lumen per square foot	fc	≡ lm/ft^2	= 10.763910417 lx
lumen per square inch	lm/in^2	≡ lm/in^2	≈ 1550.0031 lx
lux (SI unit)	lx	≡ lm/m^2	= 1 lx = 1 lm/m^2
phot (CGS unit)	ph	≡ lm/cm^2	= 10^4 lx

Radiation – source activity

Radioactivity

Name of unit	Symbol	Definition	Relation to SI units
becquerel (SI unit)	Bq	≡ Number of disintegrations per second	= 1 Bq = 1/s
curie	Ci	≡ 3.7×10^10 Bq[43]	= 3.7×10^10 Bq
rutherford (H)	Rd	≡ 1 MBq	= 10^6 Bq

Although becquerel (Bq) and hertz (Hz) both ultimately refer to the same SI base unit (s⁻¹), Hz is used only for periodic phenomena (i.e. repetitions at regular intervals), and Bq is only used for stochastic processes (i.e. at random intervals) associated with radioactivity.[44]

Radiation – exposure

Radiation - exposure

Name of unit	Symbol	Definition	Relation to SI units
roentgen	R	1 R ≡ 2.58×10^−4 C/kg[37]	= 2.58×10^−4 C/kg

The roentgen is not an SI unit and the NIST strongly discourages its continued use.[45]

Radiation – absorbed dose

Radiation - absorbed dose

Name of unit	Symbol	Definition	Relation to SI units
gray (SI unit)	Gy	≡ 1 J/kg = 1 m^2/s^2 [46]	= 1 Gy
rad	rad	≡ 0.01 Gy[37]	= 0.01 Gy

Radiation – equivalent dose

Radiation - equivalent dose

Name of unit	Symbol	Definition	Relation to SI units
Röntgen equivalent man	rem	≡ 0.01 Sv	= 0.01 Sv
sievert (SI unit)	Sv	≡ 1 J/kg[44]	= 1 Sv

Although the definitions for sievert (Sv) and gray (Gy) would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation (given as Gy) is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented as

H = Q ⋅ D

where H is the equivalent dose, D is the absorbed dose, and Q is a dimensionless quality factor. Thus, for any quantity of D measured in Gy, the numerical value for H measured in Sv may be different.[47]

See also

• Accuracy and precision
• Conversion of units of temperature
• English units
• False precision
• Imperial units
• International System of Units
• Mesures usuelles
• Metric prefix (e.g. "kilo-" prefix)
• Metric system
• Natural units
• Orders of Magnitude
• Rounding
• Significant figures
• Unified Code for Units of Measure
• United States customary units
• Unit of length
• Units (software)
• Units conversion by factor-label
• Units of measurement

Notes and references

1. Béla Bodó; Colin Jones (26 June 2013). Introduction to Soil Mechanics. John Wiley & Sons. pp. 9–. ISBN 978-1-118-55388-6.
2. "Identity property of multiplication". Retrieved 2015-09-09.
3. David V. Chadderton (2004). Building Services Engineering. Taylor & Francis. pp. 33–. ISBN 978-0-415-31535-7.
4. Foot, C. J. (2005). Atomic physics. Oxford University Press. ISBN 978-0-19-850695-9.
5. jobs (September 14, 2012). "The astronomical unit gets fixed : Nature News & Comment". Nature.com. doi:10.1038/nature.2012.11416. Retrieved August 31, 2013. Cite journal requires |journal= (help)
6. "NIST Reference on Constants, Units, and Uncertainty."(2010). National Institute of Standards and Technology. Retrieved October 17, 2014.
7. "NIST - National Institute of Standards and Technology". NIST.
8. Lide, D. (Ed.). (1990). Handbook of Chemistry and Physics (71st ed). Boca Raton, FL: CRC Press. Section 1.
9. National Bureau of Standards. (June 30, 1959). Refinement of values for the yard and the pound. Federal Register, viewed September 20, 2006 at National Geodetic Survey web site.
10. "International Astronomical Union - IAU". www.iau.org.
11. Klein, Herbert Arthur. (1988). The Science of Measurement: a Historical Survey. Mineola, NY: Dover Publications 0-4862-5839-4.
12. The International System of Units, Section 2.1 (8 ed.), Bureau International des Poids et Mesures, 2006, archived from the original on October 1, 2009, retrieved August 26, 2009
13. International System of Units, Archived August 21, 2008, at the Wayback Machine 8th ed. (2006), Bureau International des Poids et Mesures, Section 4.1 Table 8.
14. Cox, Arthur N., ed. (2000). Allen's Astrophysical Quantities (4th ed.). New York: AIP Press / Springer. Bibcode:2000asqu.book.....C. ISBN 0387987460.
15. Binney, James; Tremaine, Scott (2008). Galactic Dynamics (2nd ed.). Princeton, NJ: Princeton University Press. Bibcode:2008gady.book.....B. ISBN 978-0-691-13026-2.
16. P. Kenneth Seidelmann, Ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. p. 716 and s.v. parsec in Glossary.
17. Whitelaw, Ian. (2007). A Measure of All Things: The Story of Man and Measurement. New York: Macmillan 0-312-37026-1. p. 152.
18. De Vinne, Theodore Low (1900). The practice of typography: a treatise on the processes of type-making, the point system, the names, sizes, styles and prices of plain printing types 2nd ed. New York: The Century Co. p. 142–150.
19. Pasko, Wesley Washington (1894). American dictionary of printing and bookmaking. (1894). New York: Howard Lockwood. p. 521.
20. Rowlett, Russ (2005), How Many? A Dictionary of Units of Measurement
21. Thompson, A. and Taylor, B.N. (2008). Guide for the Use of the International System of Units (SI). National Institute of Standards and Technology Special Publication 811. p. 57.
22. US Code of Federal Regulations, Title 21, Section 101.9, Paragraph (b)(5)(viii), archived from the original on August 13, 2009, retrieved August 29, 2009
23. Barry N. Taylor, Ed.,NIST Special Publication 330: The International System of Units (SI) (2001 Edition), Washington: US Government Printing Office, 43,"The 12th Conference Generale des Poids et Mesures (CGPM)...declares that the word "litre" may be employed as a special name for the cubic decimetre".
24. CODATA Value: atomic unit of mass. (2010). National Institute of Standards and Technology. Retrieved 29 May 2015.
25. The Swiss Federal Office for Metrology gives Zentner on a German language web page "Archived copy". Archived from the original on 2006-09-28. Retrieved 2006-10-09.CS1 maint: archived copy as title (link) and quintal on the English translation of that page "Archived copy". Archived from the original on 2001-03-09. Retrieved 2006-10-09.CS1 maint: archived copy as title (link); the unit is marked "spécifiquement suisse !"
26. Pedersen O. (1983). "Glossary" in Coyne, G., Hoskin, M., and Pedersen, O. Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary. Vatican Observatory. Available from Astrophysics Data System.
27. Richards, E.G. (1998), Mapping Time, Oxford University Press, pp. 94–95, ISBN 0-19-850413-6
28. Steel, Duncan (2000), Marking Time, John Wiley & Sons, p. 46, ISBN 0-471-29827-1
29. "CODATA Value: Planck time". physics.nist.gov. Retrieved 2018-06-20.
30. Richards, E. G. (2013). "Calendars" in S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac. Mill Valley, CA: University Science Books.
31. Richards, E. G. (2013). "Calendars" in S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac. Mill Valley, CA: University Science Books. p. 587.
32. Tom Benson. (2010.) "Mach Number" Archived 2006-04-10 at the Wayback Machine in Beginner's Guide to Aeronautics. NASA.
33. CODATA Value: atomic unit of force. (2006). National Institute of Standards and Technology. Retrieved September 14, 2008.
34. Comité International des Poids et Mesures, Resolution 2, 1946, retrieved August 26, 2009
35. Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: US Government Printing Office, pp. 57–68.
36. Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: US Government Printing Office, p. 5.
37. NIST Guide to SI Units, Appendix B.9, retrieved August 27, 2009
38. International System of Units, Archived July 16, 2012, at the Wayback Machine 8th ed. (2006), Bureau International des Poids et Mesures, Section 4.1 Table 7.
39. The NIST Reference on Constants, Units, and Uncertainty, 2006, retrieved August 26, 2009
40. Robert G. Mortimer Physical chemistry,Academic Press, 2000 ISBN 0-12-508345-9, page 677
41. Standard for the Use of the International System of Units (SI): The Modern Metric System IEEE/ASTM SI 10-1997. (1997). New York and West Conshohocken, PA: Institute of Electrical and Electronics Engineers and American Society for Testing and Materials. Tables A.1 through A.5.
42. The NIST Reference on Constants, Units, and Uncertainty, retrieved August 28, 2009
43. Ambler Thompson & Barry N. Taylor. (2008). Guide for the Use of the International System of Units (SI). Special Publication 811. Gaithersburg, MD: National Institute of Standards and Technology. p. 10.
44. The International System of Units, Section 2.2.2., Table 3 (8 ed.), Bureau International des Poids et Mesures, 2006, archived from the original on June 18, 2007, retrieved August 27, 2009
45. The NIST Guide to the SI (Special Publication 811), section 5.2, 2008, retrieved August 27, 2009
46. Ambler Thompson & Barry N. Taylor. (2008). Guide for the Use of the International System of Units (SI). Special Publication 811. Gaithersburg, MD: National Institute of Standards and Technology. p. 5.
47. Comité international des poids et mesures, 2002, Recommendation 2, retrieved August 27, 2009

Notes

1. The technical definition of tropical year is the period of time for the ecliptic longitude of the Sun to increase 360 degrees. (Urban & Seidelmann 2013, Glossary, s.v. year, tropical)

External links

• Statutory Instrument 1995 No. 1804 Units of measurement regulations 1995 From legislation.gov.uk
• "NIST: Fundamental physical constants — Non-SI units" (PDF). Archived from the original (PDF) on 2016-12-27. Retrieved 2004-03-15. (35.7 KB)
• NIST Guide to SI Units Many conversion factors listed.
• The Unified Code for Units of Measure
• Units, Symbols, and Conversions XML Dictionary
• Units of Measurement Software at Curlie
• Units of Measurement Online Conversion at Curlie