Fan CFM Airflow Calculator
Calculate required fan CFM (cubic feet per minute) for rooms, server rooms, workshops, and electronic enclosures.
Convert between CFM, CMH, and m³/min.
CFM (Cubic Feet per Minute) is the standard unit used to measure airflow rate in ventilation and cooling systems. Choosing the right fan size ensures adequate air exchange, temperature control, and equipment longevity.
The Basic Airflow Formula
For room ventilation:
Required CFM = Room Volume (ft³) × Air Changes Per Hour (ACH) / 60
Or equivalently: Required CMH (m³/h) = Room Volume (m³) × ACH
Where ACH is the number of times per hour the entire volume of air in the space should be replaced.
Recommended Air Changes Per Hour (ACH)
| Space Type | Recommended ACH |
|---|---|
| Bedroom | 6 |
| Living room / Office | 6–8 |
| Kitchen | 15–20 |
| Bathroom | 8–15 |
| Server room / Data center | 20–60 |
| Workshop with dust | 20–30 |
| Electronics enclosure (heat-critical) | Calculate from heat load |
| Grow room | 30–60 |
| Garage | 6–8 |
Electronic Enclosure Cooling
For cooling electronics based on heat dissipation:
Required CFM = (P × 3.16) / ΔT
Where:
- P = Power dissipated as heat (Watts)
- ΔT = Allowable temperature rise (°C), typically 10–20°C
- 3.16 = conversion constant for standard air at sea level
This gives you the minimum airflow to keep components at a safe temperature.
Unit Conversions
- 1 CFM = 0.0283 m³/min = 1.699 m³/h (CMH)
- 1 CMH = 0.589 CFM
- 1 m³/min = 35.31 CFM
Practical Note
Always add a 20–30% margin to your calculated CFM requirement. Fan performance curves show that rated CFM is measured at zero static pressure, meaning a bare fan in open air with nothing attached. Real system resistance cuts that by 20 to 50%. Flexible duct is the usual culprit, and every bend costs you again. If the run is long or the filter is fine, take the upper end of that range rather than the lower.
The intake matters as much as the fan
A fan can only push out what it can pull in. Seal a room, fit a 400 CFM extractor, and you will not get 400 CFM: you get whatever leaks in around the door, and the fan spends its life fighting a partial vacuum it cannot win. Passive intake vents should have roughly twice the free area of the exhaust opening. This is the single most common mistake in grow tents and workshop extraction, and it shows up as a fan that is clearly running hard while the air inside stays stale.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.