Duct Sizing Calculator

Calculate the required duct diameter for a given airflow and maximum velocity using the equal friction method.

CFM
ft/min

Round Duct Diameter

10.2 in

Cross-Section Area82.3 sq in
Actual Velocity at Next Size606 ft/min

Round Duct Diameter vs Airflow

सूत्र देखें →

सूत्र

## Duct Sizing by Velocity **A = CFM / Velocity** **Diameter = 2 x sqrt(A / pi)** Convert the area to diameter for round ducts. For residential trunk lines, maximum velocity of 700 ft/min keeps noise low. Branch runs can go up to 600 ft/min. Round up to the next standard duct size.

हल किया गया उदाहरण

400 CFM at a max velocity of 700 ft/min.

  1. 01Area = 400 / 700 = 0.571 sq ft = 82.3 sq in
  2. 02Diameter = 2 x sqrt(0.571 / pi) x 12 = 10.2 in
  3. 03Use a 10-inch round duct (or 12-inch for lower velocity).