Case Fan CFM Calculator
Estimate the airflow in CFM a PC or electronics case needs to hold a target temperature rise, and how many fans it takes.
How it works
CFM ≈ 1.76 × watts ÷ ΔT(°C) · Rated CFM = CFM ÷ efficiency · Fans = ceil(rated CFM ÷ per-fan CFM)
Moving air carries heat away, and the airflow needed rises with the heat load and falls as you allow a larger temperature difference between the case and the room. The 1.76 factor comes from the density and heat capacity of air at sea level, converting watts and a Celsius rise into cubic feet per minute. Fans never move their rated airflow inside a real case — grills, dust filters, cramped routing and back-pressure cut it, so dividing by an efficiency factor tells you the rated CFM to actually buy.
Worked example
To carry 350 W within a 10 °C rise you need 1.76 × 350 ÷ 10 ≈ 62 CFM of real airflow. At 60% efficiency that means about 62 ÷ 0.6 ≈ 103 CFM of rated fans — two 60 CFM fans cover it.
Frequently asked questions
Is more airflow always better?
Up to a point. Once components stay below their limits, extra airflow mainly adds noise and dust. Aim for enough CFM to hold your target temperature rise, then favour quieter, larger fans over high-RPM ones.
Why divide by an efficiency factor?
Manufacturers rate fans in free air with nothing in the way. Inside a case with intake filters, grills and obstructed paths, real airflow is often only 50–70% of the rating, so you size the rated CFM higher to hit the airflow you actually need.
Does this apply to any enclosure?
Yes — the formula is general for forced-air cooling of any sealed-ish box, from a PC to a networking or amplifier enclosure. Just use the heat dissipated inside and the temperature rise you can tolerate.
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This calculator is for educational purposes. Double-check important results before acting on them.