Air Velocity Calculator

Calculate how fast air is moving through a duct given CFM and duct area.

Air Velocity Calculator

Airflow (CFM)

Duct Area (sq ft)

Air Velocity

0.0 FPM

Enter values above and click calculate.

How It Works

This calculator determines how fast air is moving through a duct given the airflow and duct cross-sectional area. Velocity is a critical factor in duct design — too fast causes noise and pressure loss, too slow causes poor air distribution.

Air Velocity (FPM) = CFM ÷ Area (sq ft)

Where:
CFM = airflow in cubic feet per minute
Area (sq ft) = duct cross-sectional area in square feet
FPM = air velocity in feet per minute

Recommended velocity ranges:
Main trunk ducts: 600–900 FPM
Branch ducts: 400–700 FPM
Return air ducts: 400–600 FPM
Supply registers: 300–500 FPM

Common example: 1,200 CFM through a duct with 1.5 sq ft of cross-sectional area results in 800 FPM — well within the recommended range for a main trunk.