Skip to content
Log in Calculators

Duct Size Calculator

Round duct diameter from CFM and design velocity.

Inputs

Inputs and assumptions

Airflow for this run.

600 quiet branch, 800 supply trunk, up to 1200 return. Verify the final layout per ACCA Manual D at about 0.08 in. w.c. friction rate.

Result

Duct area (sq in)
—
Round duct diameter (in)
—

What to check

  • Airflow per run
  • Trunk vs branch velocity choice

Related calculators

Round-duct screening from the continuity equation (area = CFM / velocity). Verify fittings, equivalent lengths, and the final layout per ACCA Manual D before ordering material.

Saved calculations

Keep the assumptions with the result.

Save this calculation to return to the inputs, result, and report anytime.

Sign in to save Create account

Sign in or create an account to save this calculation.