Duct Size Calculator
Enter airflow, target velocity, and a rectangular aspect ratio. Results are arithmetic estimates for early sizing only.
A QUICK WALKTHROUGH
How to use this tool
- Airflow
- Target velocity
- Calculate
Area = airflow ÷ velocity; round diameter = √(4 × area ÷ π); for ratio r, height = √(area ÷ r) and width = r × height.
Use matching units: airflow as volume per time and velocity as distance per the same time unit. The calculated area follows those units.
Theoretical arithmetic only. This does not approve HVAC design, noise, pressure drop, code compliance, equipment selection, or safety.
Theoretical arithmetic only. This does not approve HVAC design, noise, pressure drop, code compliance, equipment selection, or safety.
Inputs stay in this browser; nothing is sent.
Inputs stay in this browser; nothing is sent.
GOOD TO KNOW
Common questions
Duct Size Calculator
Theoretical arithmetic only. This does not approve HVAC design, noise, pressure drop, code compliance, equipment selection, or safety.