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Friction Loss
Water-pipe friction loss by Hazen-Williams or by Darcy-Weisbach with the Colebrook friction factor.
Example
You enter
- Method hazen-williams
- Material PVC
- Nominal size (Sch 40 PVC/steel, Type L copper, CTS CPVC/PEX) 1
- Length (ft) 100
- Flow (gpm) 10
You get
- Head loss 5.49 ft of head
- Pressure loss 2.38 psi
- Velocity 3.71
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeBoth are for water (the Darcy path uses water at 60 F and smooth pipe), not gas.
Formula or tableHazen-Williams head loss (feet of head): hL = 10.44 × L × Q^1.852 / (C^1.852 × D^4.87) with L in ft (water; English units; the NFPA-13 4.52 coefficient gives psi, feet = psi × 2.307). Darcy-Weisbach with Colebrook-White friction factor uses water properties at 60 °F.
Source and editionHazen-Williams (AWWA M11, 5th ed., by name). Darcy-Weisbach: classical fluid mechanics.
Free accessAWWA M11 licensed; principles free at engineering OCW. NIST fluid-property tables free at nist.gov.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesmethod, material, nominal_size, length_ft, flow_gpm, headLoss_ft, pressureLoss_psi, velocity_ft_s
- Hazen-Williams C-value from data/plumbing/pipe-properties.json keyed to material; AWWA M11 5th ed.AWWA M11 by name
- Water temperature 60 °F nominalengineering practice