Round Duct Size Calculator
Calculate round duct diameter from CFM and velocity. Free, instant.
How to Use Round Duct Size Calculator
1
Enter required airflow.
2
Enter max velocity.
3
Get duct diameter.
Frequently Asked Questions
Standard duct sizes?
4, 5, 6, 7, 8, 10, 12, 14, 16 inches. Round up to nearest standard.