Pipe Head Loss Calculator (Darcy-Weisbach)

Calculate major head loss in pipes due to friction using the Darcy-Weisbach equation.

Fluid Mechanics II

Inputs

Pipe length L (m)

Internal diameter D (mm)

Flow velocity V (m/s)

Darcy friction factor f (dimensionless)

Laminar (Re < 2 300): f = 64/Re · Turbulent: use Moody chart

Theory

Darcy-Weisbach equation:

hf = f × (L/D) × (V² / (2g)) [m]

Velocity head:

hv = V² / (2g) [m] → hf = f × (L/D) × hv

Where:

hf = major head loss due to pipe friction [m]
f = Darcy friction factor (dimensionless)
L = pipe length [m]
D = internal pipe diameter [m]
V = mean flow velocity [m/s]
g = gravitational acceleration = 9.81 m/s²

Friction factor:

Laminar (Re < 2 300): f = 64 / Re
Turbulent: Moody chart or Colebrook-White equation
This is the Darcy friction factor — 4× the Fanning friction factor

Head loss represents energy dissipated by friction per unit weight of fluid. It grows linearly with pipe length and friction factor, and quadratically with velocity — doubling V quadruples hf.