How do I calculate cfm? CFM = BTU/hr ÷ (1.08 × ΔT). Enter your numbers above and the result updates instantly. For example: Heat load: 36,000 BTU/hr · Temperature difference (ΔT): 20 °F → Required airflow: 1,667 CFM.
Is this CFM Calculator free? Yes — completely free with no sign-up or paywall. It runs entirely in your browser and keeps working offline; the numbers you enter never leave your device.
How accurate is it? It uses the standard published formula for cfm. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.