Duct Size Calculator by CFM
Duct size by CFM converts airflow into required duct area, round diameter or rectangular dimensions using velocity or equal-friction targets.
duct size calculator by cfm cfm duct size calculator round duct cfm
Area from CFM
A = Q / v
Round equivalent
D = sqrt(4 * A / pi)
Friction follow-up
After choosing duct size, add equivalent length and fittings in the duct friction loss calculator before checking the blower static-pressure budget.
Related pages
- Duct size calculator - round and rectangular duct sizing from airflow.
- Duct friction loss calculator - run-level pressure loss from duct size and length.
- HVAC static pressure calculator - total external static pressure and blower margin.
- Grille size calculator - face velocity and free-area checks for terminals.