Formula & example
Vfpm=CFM/Aft²; Vm/s=Vfpm·0.00508.
400 CFM through a 10 in round duct is about 733 fpm or 3.72 m/s.
HVAC engineering calculator · Updated Sep 17, 2026
Duct Velocity Calculator — CFM, FPM & Air Speed
Calculate air velocity from CFM and round or rectangular duct dimensions, with FPM and m/s outputs.
Inputs
Result
Duct 10 in round
Area 78.539816 in²
Velocity 733.38598 fpm
Velocity 3.7256008 m/s
Airflow 679.60433 m³/h
Assumptions & limits
- Free internal duct dimensions are used.
- The calculation is cross-sectional average velocity, not a local traverse profile.
Frequently asked questions
What does this Duct Velocity Calculator calculate?
Calculate air velocity from CFM and round or rectangular duct dimensions, with FPM and m/s outputs.
Can I use SI and US customary units?
Yes. The calculator exposes the unit basis in the inputs and reports useful cross-unit outputs where the engineering workflow benefits from them.
Is this a replacement for HVAC design software?
No. It is a transparent deterministic engineering calculator for sizing, diagnostics and cross-checks. Final equipment, duct and refrigeration decisions should use measured conditions, manufacturer data and applicable codes or standards.