Duct design
Duct Velocity Calculator
Calculate velocity in a round duct from CFM and diameter.
Round duct calculator
How to use
Enter airflow and the inside diameter of a round duct. For a rectangular duct, calculate face area first and divide CFM by area in square feet.
Formula
Velocity (FPM) = CFM ÷ duct area (ft²)
Variables
Velocity is feet per minute; duct area is the interior face area.
Example
600 CFM through a 14 in round duct produces approximately 561 FPM.
Result interpretation
Use project-specific acoustic, pressure-drop, and code criteria to judge velocity.
FAQ
Does this calculate pressure loss?
No. Pressure loss also depends on duct length, fittings, surface, and air properties.