HVAC Design Tool
HVAC Duct Calculator
Interactive duct sizing tool for airflow, friction rate, velocity, round duct, and rectangular duct design.
HVAC DESIGN TOOL
HVAC Duct Calculator
Interactive equal-friction airflow and velocity calculator
Galvanized round duct · standard air
Drag the friction ring to change airflow. The friction and velocity scales are calibrated to the same equal-friction relationship.
How to Use the HVAC Duct Calculator
Enter airflow and friction rate to determine an equivalent round duct size, velocity, and practical rectangular duct options.
What This Calculator Provides
- Round duct diameter
- Suggested nominal duct size
- Air velocity
- Friction rate
- Equivalent rectangular duct dimensions
Equal Friction Method
The equal friction method sizes ductwork around a consistent friction rate while maintaining the airflow required by the system.