PC Case Airflow Calculator
Case fan CFM for a PC build.
Enter your values
Enter the total heat output in W.
Enter the acceptable temperature rise in °C.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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.
CFM = watts x 3.412 / (1.08 x ΔT °F)
At a glance
| What it does | Case fan CFM for a PC build. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Total heat output, Acceptable temperature rise |
| Main output | Required airflow |
| Formula | CFM = watts x 3.412 / (1.08 x ΔT °F) |
| Cost | Free — no sign-up, no download |
How to use the PC Case Airflow Calculator
- 1Add up CPU, GPU and other component power under load.
- 2Pick an acceptable rise over ambient — 8-12°C is typical for a good build.
- 3Buy roughly 50% more rated fan CFM than calculated, since case restriction cuts real flow.
Inputs explained
- Total heat output(W)
- Enter the total heat output in W.
- Acceptable temperature rise(°C)
- Enter the acceptable temperature rise in °C.
Worked example
Using the values the calculator loads with:
Inputs
- Total heat output450 W
- Acceptable temperature rise10 °C
Results
- 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
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.
What do I need to enter into the PC Case Airflow Calculator?
Just 2 values: total heat output, acceptable temperature rise. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the PC Case Airflow Calculator work out the answer?
PC case airflow follows the same sensible heat equation as HVAC — watts of heat divided by 1.08 times the temperature rise. It applies the formula CFM = watts x 3.412 / (1.08 x ΔT °F) and shows the working so you can check each step by hand.
Is the PC Case Airflow Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.