Friction Loss

Hazen-Williams for water; Darcy-Weisbach for gas.

Run the calculator

Example

You enter

Method hazen-williams
Material PVC
Nominal Sch 40 size 1
Length (ft) 100
Flow (gpm) 10

You get

Head loss 5.49 ft of head
Pressure loss 2.38 psi
Velocity 3.71

Details, formula, and sources

Hazen-Williams head loss (feet of head): hL = 10.44 × Q^1.852 / (C^1.852 × D^4.87) per 100 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.

Hazen-Williams (AWWA M11, 5th ed., by name). Darcy-Weisbach: classical fluid mechanics.

AWWA M11 licensed; principles free at engineering OCW. NIST fluid-property tables free at nist.gov.

Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

Field names used by the API: method, 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