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Duct sizing and airflow calculators
Free duct sizing and airflow calculators, computed live from Darcy-Weisbach and Swamee-Jain, not scanned charts. Everything runs on your device, nothing you enter is uploaded.
All tools · 9 of 9
Duct Sizing
Flexible Duct CFM Chart & Sizing Calculator
CFM capacity and required diameter for flex duct, computed from Darcy-Weisbach.
Round Duct Sizing Chart & CFM Calculator
CFM capacity and required diameter for round galvanized duct, computed from Darcy-Weisbach.
Rectangular Duct Sizing Chart & Calculator
Rectangular duct sizing via Huebscher equivalent diameter, wired to the round-duct solver.
Duct Velocity & Friction Loss Calculator
Check an existing round or rectangular duct: velocity, friction rate, and total loss by material.
Grille & Register Sizing Calculator
Size a supply or return grille from CFM, face velocity, and your grille's free-area ratio.
Fan Velocity Pressure & Affinity Law Calculator
Convert velocity to velocity pressure, and predict CFM/SP/HP at a new fan speed.
Return Duct Sizing Chart & Calculator
Return duct sizing at a quieter, return-appropriate velocity target, round or rectangular.