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Calculation Machine

PC Case Airflow Calculator

Case fan CFM for a PC build.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Required airflow
79 CFM
With 50% real-world derate
118.5 CFM of fan rating
120mm fans at 55 CFM
3
Heat in BTU/h
1,535
Rise in °F
18

Quick answer

PC case airflow follows the same sensible heat equation as HVAC — watts of heat divided by 1.08 times the temperature rise.

The formula

CFM = watts x 3.412 / (1.08 x ΔT °F)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Total heat output450 W
  • Acceptable temperature rise10 °C

Result

  • Required airflow79 CFM
  • With 50% real-world derate118.5 CFM of fan rating
  • 120mm fans at 55 CFM3
  • Heat in BTU/h1,535
  • Rise in °F18

How to use the PC Case Airflow Calculator

  1. 1Add up CPU, GPU and other component power under load.
  2. 2Pick an acceptable rise over ambient — 8-12°C is typical for a good build.
  3. 3Buy roughly 50% more rated fan CFM than calculated, since case restriction cuts real flow.

Frequently asked questions

Positive or negative pressure?

Slight positive pressure with filtered intakes keeps dust out and performs about the same thermally.

Static pressure fans?

Use them on radiators and restrictive filters; airflow-optimised fans suit open case panels.

About this calculator