Hazen-Williams Calculator – Head Loss

What this calculator does

Calculates water-pipe head loss using the Hazen–Williams equation. It is a practical empirical correlation for ordinary water distribution, not a general fluid-friction law.

Inputs

Flow rate m³/h

Inside diameter mm

Pipe length m

Hazen–Williams C

Use a value appropriate to pipe material, age and condition.

Water density kg/m³

Flow, diameter, C-factor and density must be positive; length cannot be negative.

Results

Head loss

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Pressure drop

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Velocity

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Hydraulic gradient

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Applicability: Use for water in conventional distribution piping; use Darcy–Weisbach for other fluids or rigorous temperature/viscosity treatment.

What Hazen–Williams estimates

Hazen–Williams is an empirical equation for friction head loss in water piping. Its C-factor represents the observed hydraulic smoothness of the pipe and its condition.

Why it remains common

The method is simple and is widely used for water-distribution and fire-water networks. It avoids a separate Reynolds-number and friction-factor solution when its empirical range is appropriate.

How the SI equation works

This page uses hL = 10.67 LQ^1.852/(C^1.852 D^4.8704), with Q in m³/s and D in metres internally. A larger flow or smaller diameter increases loss strongly; a larger C-factor reduces the predicted loss.

Choosing a C-factor

Use values from the governing design basis, utility standard or reliable condition assessment. Age, deposits, corrosion, lining and tuberculation can reduce effective C, so a new-pipe value may be unconservative for an old system.

Limits of the method

Use it for ordinary water service within accepted practice. It is not a universal law for oils, gases, slurries or strongly temperature-dependent fluids. Darcy–Weisbach is the more general method when viscosity and roughness must be represented physically.

Hazen–Williams Calculator