Cubic inch

The cubic inch (symbol in3) is a unit of volume in the Imperial units and United States customary units systems. It is the volume of a cube with each of its three dimensions (length, width, and depth) being one inch long which is equivalent to 1/231 of a US gallon.[1]

Cubic inch
An engine with a swept piston displacement of 502 cubic inches.
General information
Unit systemNonstandard
Unit ofvolume
Symbolin3 or cu in 
Conversions
1 in3 in ...... is equal to ...
   SI derived units   ≈ 16.387 mL
   US customary   ​1⁄231 US Gallon
   nonstandard   ​1⁄1728 ft3

The cubic inch and the cubic foot are used as units of volume in the United States, although the common SI units of volume, the liter, milliliter, and cubic meter, are also used, especially in manufacturing and high technology. One cubic inch is approximately 16.387 mL.

One cubic foot is equal to exactly 1,728 cubic inches because 123 = 1,728.

One U.S. gallon is equal to exactly 231 cubic inches because 3 * 7 * 11 = 231.

Notation conventions

The following abbreviations have been used to denote the cubic inch:

  • cubic in, cu inch, cu in, cui, CI, c.i.
  • inch³, in³

In internal combustion engines, the following abbreviations are used to denote cubic inch displacement:

  • c.i.d., cid, CID

Equivalence with other units of volume

1 cubic inch (assuming an international inch) is equal to:

  • 0.000578703703703 cubic feet (1 cu ft equals 1,728 cu in)
  • roughly 1 tablespoon (1.0 U.S. gallon = 256 U.S. tablespoons = 231 cubic inches)
  • about 0.554112552 American/English fluid ounces
  • about 0.069264069 American/English cups
  • about 0.000465025413 American/English bushels
  • about 0.004329 American liquid gallons (1.0 gallon equals 231 cu in exactly [3 in × 7 in × 11 in])
  • about 0.00010307 barrels of crude oil (1.0 barrel equals 42 gallons, by definition, or 9,702 cu in)
  • exactly 0.016387064 liter (1.0 liter is about 61 cu in [exactly 61.0237440947323 cu in])
  • exactly 16.387064 milliliters or cubic centimeters (which in turn is approximately 0.061 cu in)
  • exactly 0.000016387064 cubic meters (1.0 m³ is about 61,023.74 cu in)

Uses of the cubic inch

Electrical box volume

The cubic inch was established decades ago as the conventional unit in North America for measuring the volume of electrical boxes. Because of the extensive export of electrical equipment to other countries, some usage of the non-SI unit can be found outside North America.

Engine displacement
Main article: Engine displacement

North America

The cubic inch was formerly used by the automotive industry and aircraft industry in North America (through the early 1980s) to express the nominal engine displacement for the engines of new automobiles, trucks, aircraft, etc. The cubic inch is still used for this purpose in classic car collecting. The auto industry now uses liters for this purpose, while reciprocating engines used in commercial aircraft often have model numbers based on the cubic inch displacement. The fifth generation Ford Mustang has a Boss 302 version that reflects this heritage - with a five-liter (302 cubic inch) engine similar to the original Boss. Chevrolet has also revived this usage on its 427 Corvette. Dodge has a "Challenger 392" (a conversion from its 6.4 liter V8 engine).

United Kingdom

In the UK, engine displacement is now denoted in litres. However, cubic inches were sometimes used in the past to denote model numbers. An example is the AEC Reliance bus which was available with five different engines:

  • AH470, 470 cubic inches, 7.7 litres = 1.6942 gallons
  • AH505, 505 cubic inches, 8.1 litres = 1.8203 gallons
  • AH590, 590 cubic inches, 9.6 litres = 2.1267 gallons
  • AH691, 691 cubic inches, 11.3 litres = 3.5925 gallons
  • AH760, 760 cubic inches, 12.4 litres = 3.9512 gallons
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See also

References
  1. "260.1-2004 - IEEE Standard Letter Symbols for Units of Measurement (SI Customary Inch-Pound Units, and Certain Other Units)". standards.ieee.org. Retrieved 22 December 2019.
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