// Free tool · Ductulator
Size it.
Then let us build it.
Enter your airflow and design friction rate or velocity. You'll get the round size, equivalent rectangular sizes, velocity and velocity pressure.
Round (exact)–
Next standard–
Velocity–
Friction /100 ft–
Velocity pressure–
Equivalent rectangular
| Size | Aspect | De | FPM | in./100ft |
|---|
Estimates only, for standard galvanized steel duct at standard air (70°F, sea level, 0.075 lb/ft³). The calculator uses the ASHRAE friction-chart approximation and the equivalent-diameter formula De = 1.30(ab)0.625/(a+b)0.25. Verify final sizing with your engineer of record.