What is the Darcy-Weisbach equation?

h_f = f · (L/D) · V²/(2g), where h_f is friction head loss (m), f is the Darcy friction factor (dimensionless), L is pipe length (m), D is inner diameter (m), V is mean velocity (m/s), and g is gravitational acceleration (9.81 m/s²). Pressure drop ΔP = ρ · g · h_f.

How is the friction factor calculated?

For laminar flow (Re < 2300), f = 64/Re exactly. For turbulent flow, this calculator uses the Colebrook-White implicit equation — 1/√f = −2 log₁₀(ε/(3.7D) + 2.51/(Re√f)) — solved iteratively with Newton-Raphson convergence to six significant figures.

What pipe roughness value should I use?

Typical absolute roughness (ε): drawn copper/brass tubing ≈ 0.0015 mm, commercial steel ≈ 0.046 mm, galvanized steel ≈ 0.15 mm, cast iron ≈ 0.26 mm, concrete ≈ 0.3–3 mm. PVC and smooth plastic pipes are often treated as hydraulically smooth (ε ≈ 0.0015 mm).

Does this include minor losses (fittings, bends, valves)?

No. This calculator covers major (straight-pipe friction) losses only. Minor losses from fittings, valves, and bends must be added separately using K-factor or equivalent-length methods.

What is the difference between head loss and pressure drop?

Head loss (m) is the energy loss expressed as an equivalent height of fluid column — it is fluid-independent in that sense. Pressure drop (Pa or psi) converts head loss back to pressure using ΔP = ρ · g · h_f, so it depends on fluid density.

Pipe Friction Loss Calculator

Name: Pipe Friction Loss Calculator
Availability: InStock
Author: Nham Vu

Enter pipe geometry, flow rate, and fluid properties to calculate friction head loss and pressure drop using the Darcy-Weisbach equation.

Pipe & Flow Parameters

Unit System

Pipe Inner Diameter (mm)

Pipe Length (m)

Wall Roughness ε (mm)

Volumetric Flow Rate (L/s)

Fluid

Results

Enter parameters and click Calculate.

Summary