Duct Friction Loss Calculator

Calculate pressure drop per 100 feet of straight ductwork using the Darcy-Weisbach equation. Essential for duct system design and fan selection.

Volume flow rate of air through the duct.
CFM
Width of rectangular duct (or diameter for round duct).
inches
Height of rectangular duct (enter same as width for round duct).
inches
Total length of straight duct run.
feet

Results

Air Velocity-FPM
Friction Loss per 100 ft-in. w.g.
Total Friction Loss-in. w.g.
Hydraulic Diameter-inches
References: ASHRAE Fundamentals Chapter 21: Duct Design; SMACNA HVAC Systems Duct Design