Duct CFM Calculator

Airflow from anemometer velocity × inside duct area

Enter a traverse-average velocity (FPM or m/s) and inside round diameter or rectangular width × height. The tool returns CFM = V × A. A single center-point reading overstates typical duct velocity — average multiple points across the cross-section first.

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How to Use This Duct CFM Calculator

Measure velocity with an in-duct anemometer using a multi-point traverse (not one center stab). Average those FPM values. Enter the average plus inside dimensions. The formula is:

CFM = Velocity (FPM) × Area (ft²) | Area_round = πd² / (4×144) | Area_rect = (W×H) / 144

Walkthrough: How to Measure Duct CFM. If the number is short of design: low/high CFM troubleshooting. In-duct vs capturing hood: Anemometer vs Flow Hood. Whether to grab a manometer first is already covered in Static Pressure vs Airflow (CFM) — use that instead of duplicating it here. High static after a low CFM? ESP calculator. Need to resize the run? Ductulator.

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Anemometers & Backup ESP Meters

From the TestTalkHQ HVAC Tools / Duct Work & Air Flow catalog — in-duct and vane anemometers for the velocity reading this calculator uses, plus manometers for the static-pressure check when CFM is short. No capturing flow hood SKU was in the CSV at publish time, so none is invented here.