What is the Darcy-Weisbach equation?

hf = f × (L/D) × (v²/2g), where hf is head loss (m or ft), f is the Darcy friction factor (dimensionless), L is pipe length, D is inner diameter, v is average flow velocity, and g is gravitational acceleration (9.81 m/s² or 32.174 ft/s²).

What is the Darcy friction factor?

A dimensionless value that captures the effect of pipe roughness and flow regime on friction. For laminar flow (Re < 2300), f = 64/Re. For turbulent flow, use the Moody chart or Colebrook-White equation. Smooth commercial steel pipes typically have f ≈ 0.010–0.020.

How do I convert head loss to pressure drop?

Pressure drop ΔP = ρ × g × hf, where ρ is fluid density (1000 kg/m³ for water) and g is 9.81 m/s². This calculator performs that conversion automatically.

What is the difference between Darcy and Fanning friction factors?

The Darcy (Moody) friction factor is 4 times the Fanning friction factor. This calculator uses the Darcy friction factor, which is more common in civil and mechanical engineering. Make sure the value you enter matches this convention.

What Reynolds number indicates turbulent flow?

Re > 4000 is fully turbulent; Re < 2300 is laminar; 2300–4000 is the transition zone. The calculator computes Re from your inputs so you can confirm the flow regime before choosing a friction factor.

Darcy-Weisbach Calculator

Name: Darcy-Weisbach Calculator
Availability: InStock
Author: Nham Vu

Calculate pressure drop and head loss in pipe flow using the Darcy-Weisbach equation.

Pipe Parameters

Unit System

Pipe Length (m)

Inner Diameter (m)

Flow Velocity (m/s)

Darcy Friction Factor (f, dimensionless)

Laminar: f = 64/Re — Turbulent: use Moody chart

Fluid Density (kg/m³)

Darcy-Weisbach Equation

h_f = f × (L / D) × (v² / 2g)

h_f = head loss (m or ft)

f = Darcy friction factor

L = pipe length

D = inner diameter

v = flow velocity

g = gravity (9.81 m/s²)

Reynolds Number Helper

Dynamic Viscosity (Pa·s)

Summary