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I recently picked up an old system with fairly noisy fans. I'd like to replace them, but the fans themselves don't have any mention of their size. Now, I know that there's standard sizes like 40, 60, 80, 92, 120 (and non standard ones, like sticking a box fan on the side of your system).
My question is, how do I measure the size? Is it by the size of the blades, or the square casing they're in?
Journeyman Geek
Posted 2011-09-12T00:31:05.633
Reputation: 119 122
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It's the length or width (doesn't matter because it's a square) of the frame in millimeters, not the blades.
Mike Rowave
Posted 2011-09-12T00:31:05.633
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You measure a computer fan along one edge, from the points where the screw holes are.
Zoredache
Posted 2011-09-12T00:31:05.633
Reputation: 18 453
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My question is, how do I measure the size? Is it by the size of the blades, or the square casing they're in?
What difference does it make? The frame is at most a few mm larger than the blades. For example, if the blades have a diameter of 76mm, then the fan is obviously an 80mm fan. Because for all intents and purposes, (ie, regular, consumer use) fans are standard sizes, so you can just round to the nearest size (there are no standard sizes that close together).
One time, I saw what I thought was a 40mm fan on a video-card which turned out to be in actuality 36mm:
Regardless, the fan itself had no frame, so with one, it would still have been a 40mm fan anyway.
Synetech
Posted 2011-09-12T00:31:05.633
Reputation: 63 242
on a case fan, it makes a difference in terms of the holes on the fan fitting the holes on the case -which need to be a precise fit – Journeyman Geek – 2011-10-17T00:29:55.620
Are you saying that a fan with 78mm blades will have different screw-holes than a fan with an 80mm frame? My point is that most general-use fans are standard sizes, and because the difference between each size is more than the difference between the blades and the frame, you can round to the nearest size to figure out the “official” size of the fan using either the blades or the frame. – Synetech – 2011-10-17T04:31:15.343
well, there are iirc, 80 and 82 mm fans - which are pretty close in size. If bringing an example fan was not an option, and i had measured the blades of a 92mm fan, it would measure as an 92 mm fan, and you'd get the wrong size. In this case, there IS a convention which is going by case size. – Journeyman Geek – 2011-10-17T06:16:32.843
But are the 82mm or 92mm fans in common use in consumer systems? How often do you come across them? For most people, rounding is sufficient. If you work in a field with proprietary sizes a commonality, then you’ll need your tape measure to measure each and every aspect since if one part is non-standard, then other parts (like the screw hole distances, spacing between blades and frame, etc) are probably non-standard as well. – Synetech – 2011-10-18T17:49:45.457
what is the size in your example? – Louis Rhys – 2011-09-12T06:24:09.100
92mm, i edited that in, as it was in a deleted answer, and while this was the most correct answer, the diagram made it clearer. – Journeyman Geek – 2011-09-12T07:23:11.220