Flex Duct CFM Capacity Chart
Flex duct CFM capacity is limited by airflow velocity, installation quality and pressure drop. Use the duct size calculator for the equivalent round size before checking friction loss.
flex duct cfm capacity chart duct size calculator by cfm round duct cfm
Velocity sizing
A = Q / v
Round duct diameter
D = sqrt(4 * A / pi)
Flex-duct caution
Sag, compression, bends, long runs and poor liner tension can make flexible duct lose more pressure than the simple size chart suggests.
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.