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Rispri LabsENGINEERING A CIRCULAR FUTURE

Free tool · Engineering calculations

Pipe Friction Head Loss Calculator

Friction head loss = f × (L ÷ D) × v² ÷ 2g (Darcy-Weisbach), with friction factor f from the Swamee-Jain equation. 10 m³/h through 100 m of 50 mm PVC pipe flows at 1.4 m/s and loses about 3.9 m of head.

Your inputs

Results update as you type. Example values are filled in.

mm

Use the inside diameter, not the nominal size.

m

90° elbow 0.3 to 0.9, gate valve open 0.2, non return valve 2, entrance 0.5, exit 1.

m

Optional. Height from water level to delivery point, for total pump head.

°C

How to use this calculator

  1. Enter the flow and the pipe inside diameter.
  2. Enter the length and choose the pipe material.
  3. Add fittings and static lift if you are sizing a pump.
  4. Read head loss, velocity and total head.

How do you calculate friction head loss in a pipe?

hf = f × (L ÷ D) × v² ÷ 2g (Darcy-Weisbach)

f = 0.25 ÷ [log₁₀(ε ÷ 3.7D + 5.74 ÷ Re0.9)]² (Swamee-Jain)

hf = 10.67 × L × Q1.852 ÷ (C1.852 × D4.87) (Hazen-Williams)

Minor loss = ΣK × v² ÷ 2g

Re = vD ÷ ν, with water viscosity from temperature. Laminar flow (Re under 2,300) uses f = 64 ÷ Re.

Worked example

With flow 10 m³/h, pipe internal diameter 50 mm, pipe length 100 m, pipe material: PVC, CPVC, HDPE (ε 0.0015 mm, C 150), sum of fitting loss coefficients (σk) 0, static lift 0 m, water temperature 25 °C:

Friction head loss: 3.86 m

The calculator also gives velocity 1.41 m/s; reynolds number 79,201 Turbulent; friction factor f 0.0189.

Assumptions and limits

  • Water only. Slurries and viscous fluids need other methods.
  • Hazen-Williams is valid for water at normal temperatures and pipes over about 50 mm.
  • Roughness grows as pipes age; use older pipe values for long term design.

Frequently asked questions

Darcy-Weisbach or Hazen-Williams?

Darcy-Weisbach works for any fluid, size and temperature and is more accurate. Hazen-Williams is simpler and widely used for municipal water mains; CPHEEO uses it for distribution network design.

What velocity should water flow at in a pipe?

Pump delivery and water mains are usually designed for 0.6 to 2.5 m/s. Suction lines should stay under about 1.5 m/s.

How do I convert head loss to pressure?

For water, 10.2 m of head is 1 bar. Multiply head in metres by 0.0981 to get bar.

References

  • Swamee and Jain (1976). Explicit equations for pipe flow problems. Journal of the Hydraulics Division, ASCE 102(5)
  • CPHEEO, Manual on Water Supply and Treatment (1999)
  • Crane Technical Paper 410, Flow of Fluids

Built and maintained by the Rispri Labs engineering team. Last updated .