Formula and input notes
Airflow (CFM) = room length × width × height × air changes per hour ÷ 60
| Input | Practical note |
|---|---|
| Target air changes | ACH is a design or operating target, not a value inferred by the calculator. Select it from the requirement that governs the space and airflow purpose. |
Worked cfm example
CFM Calculator example: 21.9 ft × 12.6 ft × 8.42 ft = 2,323.41 ft³. At 6 air changes per hour, 2,323.41 × 6 ÷ 60 = 232.34 CFM.
Interpret CFM for the selected ACH
Treat CFM as the average room airflow associated with the entered ACH, not a fan selection without static-pressure data.
Fan, duct, and outdoor-air factors outside this formula
Ceiling shape, occupied zone, supply and return placement, system leakage, filter resistance, pressurization, outdoor air, and mixing affect delivered airflow.
Questions specific to this calculation
What CFM does this calculator compute?
It computes the airflow associated with an entered room volume and air-change rate: CFM = volume × ACH / 60. It does not calculate pressure loss, fan power, diffuser throw, or duct size.
Why can supply CFM differ from an exhaust or outdoor-air requirement?
Air-change targets describe a volumetric rate, but real systems may recirculate air or require separate outdoor, exhaust, makeup, and transfer-air balances. Define which airflow the selected ACH is meant to represent.