HVAC · Problem-solving calculator
CFM Calculator
Estimate airflow in cubic feet per minute from room dimensions and a user-selected target air-change rate.
- Free to use
- Runs in your browser
- Level B · Industry formula
- Last reviewed 2026-08-17
Calculator guide
What this calculator helps you solve
Estimate airflow in cubic feet per minute from room dimensions and a user-selected target air-change rate.
Inputs explained
- Room length (ft) — enter the value that applies to your operation or scenario.
- Room width (ft) — enter the value that applies to your operation or scenario.
- Ceiling height (ft) — enter the value that applies to your operation or scenario.
- Target air changes per hour — enter the value that applies to your operation or scenario.
Formula and methodology
Worked example
A 20 × 15 × 10 foot room has 3,000 cubic feet of volume. At 6 air changes per hour, the corresponding airflow is 300 CFM.
How to interpret the result
Use the result only after determining an appropriate ACH target for the actual occupancy, process, code, standard, and ventilation strategy. ACH alone does not establish outdoor-air or load requirements.
What to keep in mind
- This is a geometric airflow conversion from a user-supplied ACH target.
- Required ventilation can depend on people, contaminants, outdoor air, exhaust, pressure relationships, and applicable codes or standards.
Review approach
This calculator uses deterministic arithmetic and performs the calculation locally in your browser. Its value comes from combining operational inputs into a decision-oriented result rather than returning a one-line conversion.
Review standard: Level B · Industry formula. How calculator reviews work.
Frequently asked questions
What decision can this calculator support?
Use the result only after determining an appropriate ACH target for the actual occupancy, process, code, standard, and ventilation strategy. ACH alone does not establish outdoor-air or load requirements.
How is the result calculated?
CFM = Room Volume × Air Changes per Hour ÷ 60.
Are the assumptions universal?
No. Operational, regulatory, technical, and industry assumptions vary. Use values that apply to your situation and verify professional or regulatory requirements where relevant.
Does CalculateMeasure store the values I enter?
The calculation runs in your browser and does not require sending the entered calculator values to a server to produce the result.