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Pressure Loss Calculator

Calculate pipe pressure loss using the Darcy–Weisbach equation for any flow, pipe size, and friction factor.

Pressure loss
40 kPa
Darcy–Weisbach: ΔP = ρ·g·hₑ, where hₑ = f·(L/D)·v²/(2g). For water, 1 m of head ≈ 9.81 kPa.
Pressure loss (bar)
0.4 bar
Head loss
4.079 m
Pressure loss (Pa)
40,000 Pa

How it works

  1. 1Enter the Darcy friction factor f, pipe length, inner diameter, and mean flow velocity.
  2. 2The calculator finds head loss hf = f·(L/D)·v²/(2g), then ΔP = ρ·g·hf (water at 1000 kg/m³).
  3. 3Results show kPa or psi, bar, metres of head, and pascals.

Use cases

  • Sizing pumps and selecting pipe diameters for water and HVAC systems.
  • Checking a pipe network can deliver flow without excessive pressure drop.
  • Verifying hand-calculated Darcy–Weisbach worked examples.

Frequently asked questions

What is the Darcy–Weisbach equation?

It gives friction head loss hf = f·(L/D)·v²/(2g); pressure loss follows as ΔP = ρ·g·hf. For water, ΔP ≈ 9.81 kPa per metre of head.

How do I find the friction factor?

For turbulent flow in smooth steel, f ≈ 0.02 is a common estimate; more precisely use the Moody chart or Colebrook–White. Laminar flow (Re < 2300) gives f = 64/Re.

Worked example: 100 m of 100 mm pipe at 2 m/s, f = 0.02?

hf ≈ 4.077 m, so ΔP = 1000 × 9.81 × 4.077 ≈ 40 kPa (≈ 0.40 bar).

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