Airflow CFM Calculator
Calculate airflow in cubic feet per minute (CFM) using either the Velocity Method (duct velocity × area) or the Air Changes Per Hour (ACH) Method (room volume ÷ 60 × ACH).
Formulas Used
Velocity Method:
CFM = Velocity (FPM) × Area (ft²)
Rectangular duct area: A = (Width × Height) / 144 (converts in² → ft²)
Circular duct area: A = π × (Diameter / 2)² / 144 (converts in² → ft²)
ACH Method:
CFM = (Room Volume (ft³) × ACH) / 60
Room Volume: V = Length × Width × Height
Assumptions & References
- The ACH Method divides by 60 to convert air changes per hour into per minute (CFM).