Darcy-Weisbach Friction Loss Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 26, 2026Darcy-Weisbach Friction Loss Calculator
Every meter of pipe a fluid travels through costs some pressure to friction against the pipe wall - the Darcy-Weisbach equation is the standard way to quantify exactly how much.
The Formula
ΔP = f × (L/D) × (ρv²/2)
Worked Example
A friction factor of 0.02, 100m of 100mm pipe, water at 1000 kg/m³ flowing at 2 m/s: ΔP = 0.02 × (100/0.1) × (1000 × 4/2) = 40,000 Pa = 40 kPa.
Frequently Asked Questions
Why does velocity matter so much more than length?
Friction loss scales with the square of velocity but only linearly with length, so doubling flow velocity through the same pipe quadruples the pressure loss, while doubling pipe length only doubles it.
Where does the friction factor come from?
It depends on Reynolds number and pipe roughness, typically read from a Moody chart or calculated from a correlation like the Colebrook equation - it is not a fixed universal constant.