HVAC Duct Calculator - Free Ductulator & CFM Tool

Input Parameters

Airflow (CFM) *

Friction Rate (in. w.g./100 ft) *

Velocity (FPM) *

Round Duct

Enter CFM to calculate

Rectangular Duct

Enter CFM to calculate

HVAC Design Quick Reference

Typical Air Velocities: Main ducts: 1000-1800 FPM - Branch ducts: 800-1400 FPM - Supply outlets: 500-750 FPM - Return air: 800-1000 FPM

Typical Friction Rates: Low velocity: 0.05-0.08 - Standard: 0.1 - High velocity: 0.15-0.2 in.w.g./100ft

ASHRAE Design Guidelines: Aspect ratios greater than 4:1 not recommended