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What Size Case Fan Do You Need? [Here’s How to Measure]

There are several sizes of PC Case fans, from 40 to 200mm fans or even more than that.

Models, like the 80mm ones, that were used in the past extensively but now no longer last in our PC Case.

In this post, I will help you know What Size Case Fan Do You Need?

How To Know What Size Case Fan You Need?

The size of the fan you need will generally be determined by the size of the fan fitting position in your PC case. The fans’ dimensions are measured with the fan’s four sides, NOT the distance between the fan’s screw holes!

The most famous fan size is 120mm, followed by 80mm. This isn’t dictated by customer preference but more by recent designs of PC cases.

Here’s you can read more about how many fans are good for your Gaming PC.

What Size Case Fan Do You Need

What Is the Normal Case Fan Size?

120mm case fans tend to be the most popular size of fans in modern PC cases, but you will find many sizes such as 80mm, 92mm, 140mm, 200mm, and beyond.

Fan size is closely related to airflow in that more giant fans will push more air than smaller ones while running at the same RPM.

This means that more giant fans can spin much more slowly than smaller ones while still pushing the same amount of air, which is excellent for lowering noise levels.

The one drawback of more giant fans is compatibility since many cases are only set up for support of 120mm and 140mm fans.

Are Case Fans Universal?

Fans can vary by bearing type (sleeve, ball, hydro), speed control type (fixed RPM, PWM, thermal RPM) and speed rating/range (900 RPM, 1200 RPM, 900-2500RPM variable, etc.), power connection (4pin Molex, 4pin PWM, 3pin, etc.) and more.

The mounting hole positions for 80mm, 92mm, and 120mm fans are standardized, so they’re primarily interchangeable (except for some Delta fans that are 38mm thick instead of 25mm, so they might not always fit in that dimension; also, they’re louder than most vacuum cleaners).

I’m not sure about 100mm or 200mm fans, and there are some heatsinks, especially from Zalman, that have non-standard fans that aren’t easily replaceable. What heatsink do you have?

How Do You Measure Case Fan Size?

The design of every computer case is different, and there are a predetermined number of slots where you can mount extra fans. The only way to find out is to open up the computer case and measure the size of those fan slots. It’s a minor hassle, but it prevents you from buying fans that won’t fit.

Standard computer case fans are square and are measured from edge to edge. For example, an 80mm fan is “just-as-it-is”, measuring 80mm from one end.

As for the fan’s thickness (depth), 25mm (1 inch) is by far the most common depth, although smaller fans can have shallower depths such as 15mm or even 10mm.

Please see the following table if you know the distance between the fan mounting screw holes but don’t know what fan size to order.

Note that the mounting hole measurements below are taken horizontally or vertically between the holes and not diagonally.

  • 32mm between screw holes 40mm fan size
  • 40mm between screw holes 50mm fan size
  • 50mm between screw holes 60mm fan size
  • 60mm between screw holes 70mm fan size
  • 72mm between screw holes 80mm fan size
  • 83mm between screw holes 92mm fan size
  • 105mm between screw holes 120mm fan size

On most modern fans, you will find 2 arrow indications:

  • The vertical arrow indicates the direction of where the blades spin.
  • The horizontal arrow indicates the airflow direction.

Don’t worry if these arrows are missing on the fan. A simple way to test the airflow direction is to put a piece of tissue in front of the fan and see which way it goes – If it gets sucked into the fan or blown away.

Are 140mm Fans better than 120mm?

Essentially, the short answer is that, on average, the more significant 140mm fan, providing that you can fit it into your PC case, is the way to go. This is because they can typically move more airflow at a lower RPM.

This means that it can keep your machine cooler and at a quieter level. This is not to say that you won’t get a good experience from a 120 mm fan; it’s just that, in general, the best way to go is the 140 mm if you have the option.

Now that you know the general rule of thumb regarding which you should go for when it comes to 120 mm vs 140 mm fans, there are a few other factors that you should take into consideration.

Of course, as you know, especially in the gaming industry, one fan from one company is certainly not the same as another company, i.e., not all fans are built alike.

I would always recommend going with a renowned brand when it comes to your cooling system rather than one you barely recognize the name of.

I would have a lot more confidence that a fan from a company like Corsair Gaming will be able to do its job. Despite having to pay potentially a bit more, I know I will get the right product for the job.

This is especially true if my PC case only caters to the smaller 120mm version.

Then finally, once you have narrowed down the top few fans that you are looking at, it could well be a mixture of 120 mm and 140 mm fans.

You will find that, especially from the leading gaming companies and specialists, it could be the case that their 120 mm outperform a lesser-known brand’s 140 mm model, yet they are around the same price.

When it comes to size, you might already be cast in a specific direction based on the capacity of your PC case.

If you can only fit in a 120mm fan, then that’s the way you’re going to go. If you haven’t got a PC case yet, you might want to consider one that can take a larger fan if you’re looking for optimum cooling efficiency relative to sound.


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