🚿 Darcy Weisbach Calculator
Calculate frictional head loss in a pipe using the Darcy-Weisbach equation, a standard fluid mechanics formula.
m
mm
m/s
What the Darcy-Weisbach equation is
The Darcy-Weisbach equation is the standard formula for calculating the head loss (energy loss due to friction) as fluid flows through a pipe.
The formula
Head loss hf = f × (L/D) × (V² / 2g), where f is the dimensionless Darcy friction factor (dependent on pipe roughness and Reynolds number, often found from a Moody chart), L is pipe length, D is pipe internal diameter, V is average flow velocity, and g is gravitational acceleration.
This calculator assumes you already know or have estimated the friction factor; getting f itself typically requires the Colebrook equation or a Moody chart based on pipe roughness and flow Reynolds number.
Last reviewed August 2026