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💧 Pipe Friction Loss Calculator

Calculate the head loss and pressure loss due to friction in a pipe using the Darcy-Weisbach equation.

💧 Pipe Friction Loss Calculator

Calculate the head loss and pressure loss due to friction in a pipe using the Darcy-Weisbach equation.

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✅ Calculation Result

Head Loss (h_f)- ft
Pressure Loss (ΔP)- psi

Losses Overview

→→→
P₁
P₂ = P₁ - ΔP
L = 100 m
D = 0.1 m

Calculator Description

Pipe friction loss is the energy a fluid loses to wall friction while flowing full in a pressurized pipe, expressed as a head loss. The Darcy-Weisbach equation is the most general and accurate way to compute it.

What this calculator finds

From pipe length L, inner diameter D, velocity v, friction factor f and fluid density ρ it computes the head loss h_f and the pressure loss ΔP. This is a key input for pump-head selection and pipe sizing.

Why it matters

  • Determining the pump head and power needed to deliver the required flow
  • Comparing how pipe diameter and velocity changes affect pressure drop (loss ∝ v²)
  • Computing pressure distribution along each segment in a pipe network

Formula

Darcy-Weisbach Equation

Head loss is proportional to the friction factor f, the length-to-diameter ratio L/D, and the velocity head v²/2g. Pressure loss is obtained by multiplying head loss by the fluid's specific weight (ρ·g).

hf=f LD v22gh_f = f\,\dfrac{L}{D}\,\dfrac{v^2}{2g}
ΔP=hf ρ g\Delta P = h_f\,\rho\,g
  • h_f — Friction head loss [m (ft)]
  • ΔP — Pressure loss [Pa (psi)]
  • f — Darcy friction factor (dimensionless; from the Moody chart)
  • L — Pipe length [m (ft)]
  • D — Inner diameter [m (in)]
  • v — Flow velocity [m/s (ft/s)]
  • ρ, g — Fluid density [kg/m³ (lb/ft³)] and gravity (9.81 m/s² or 32.174 ft/s²)

How the formula works

  • Doubling velocity quadruples the loss (∝ v²) — lowering velocity is the most effective remedy.
  • A larger diameter D shrinks both L/D and v² (=Q²/D⁴), sharply reducing loss.
  • In turbulent flow f depends on roughness and Reynolds number; in laminar flow f = 64/Re only.
  • Units: in US customary use D in ft and convert pressure via h_f×ρ (specific weight), dividing by 144 for psi.

Worked example

For water (ρ = 1000 kg/m³) in a 100 m long, 0.1 m bore pipe at 2 m/s with f = 0.02: h_f = 0.02 × (100/0.1) × (2²/(2×9.81)) ≈ 4.08 m. The pressure loss ΔP = 4.08 × 1000 × 9.81 ≈ 40 kPa.

Useful Tips

Practical tips

  • Get f from the Moody chart or Colebrook-White equation: smooth pipe ≈ 0.015–0.02, rusty steel ≈ 0.03–0.05.
  • Keep velocity in the economic range (water ≈ 1–3 m/s) to balance capital and operating cost.
  • Convert valve/elbow minor losses to equivalent length and add to L.

Limitations & cautions

  • It assumes fully developed steady laminar/turbulent flow; entrance-development regions are excluded.
  • The friction factor f changes over time with internal scale and corrosion.
  • It is for incompressible fluids (liquids); compressible-gas density change needs separate correction.