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HVAC Duct Airflow Velocity Sizing Calculator

CFM = duct area × velocity — rectangular duct sizing.

Calculates HVAC duct airflow (CFM) from rectangular duct width, height, and air velocity, and reports duct cross-sectional area.

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Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Area (ft²) = W × H / 144; CFM = Area × velocity (fpm)

In depth

Calculates HVAC duct airflow (CFM) from rectangular duct width, height, and air velocity, and reports duct cross-sectional area.