Plumbing & Fluid

Hazen-Williams Calculator

Check straight water-pipe friction using the empirical Hazen-Williams relationship. Solve head loss, flow or actual inside diameter and compare pressure and velocity without confusing bore with nominal size.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

Need an input value?

Condition- and material-dependent empirical value; replace the reference preset if necessary.

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Calculated locally in your browser. No sign-up or input upload.

YOUR CALCULATION

Results

Friction head loss

2.172 m7.126 ft

Friction pressure loss

21.262 kPa3.084 psi

Solved flow

2 L/s31.701 GPM (US)7.2 m³/h

Actual inside diameter

50 mm1.969 in

Mean water velocity

1.019 m/s3.342 ft/s

Head-loss gradient

2.172 m per 100 m
Q 2 L/sv 1.019 m/sInside diameter 50 mm
Full circular pipe bore with flow and mean velocity · schematic, not to scale

Calculation breakdown

Water-pipe model
SI Hazen-Williams · actual inside diameter · no fitting loss

Assumptions & checks

Water-oriented empirical screening model. It is not suitable for arbitrary viscous fluids, gases, partially filled drains or accurate laminar-flow design.

Results include straight-pipe friction only. Fittings, elevation and required outlet pressure belong in the Pump TDH workflow.

Formula

SI form for full, pressurized water pipes: Q in m³/s, D and L in metres. The 10.67 coefficient includes these specific unit conventions; US input is converted first.

hf = 10.67 L Q^1.852 / (C^1.852 D^4.871); Δp = ρ g hf; v = 4Q/(πD²). Reverse Q and D use the same equation algebraically.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Water flow
2 L/s
Actual inside diameter
50 mm
Straight-pipe length
100 m
Hazen-Williams C-factor
150
Water density
998.2 kg/m³

Result

Friction head loss
2.172 m
Friction pressure loss
21.262 kPa
Solved flow
2 L/s
Actual inside diameter
50 mm
Mean water velocity
1.019 m/s
Head-loss gradient
2.172 m per 100 m

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Technical references for this calculation

Reference lookupPipe Thread ReferenceReference lookupPipe Size & Schedule ChartReference lookupPlastic Pipe Size ChartReference lookupHazen-Williams C-Factor ChartReference lookupWater Properties Table

Frequently asked questions

Does this give total pump head?

No. Add static elevation, boundary pressure and fitting losses using Pump TDH. This tool isolates straight-pipe water friction.

Should diameter be the nominal pipe size?

Use actual inside diameter. A nominal size or outside diameter can differ significantly from the bore used in the equation.

Can I solve zero allowable loss?

Forward zero flow gives zero loss. Reverse flow or diameter requires a positive loss allowance to define a useful solution.

Reference data & method sources

Reference tables

EPA new-pipe C-factor reference ranges

New-pipe reference ranges, not guaranteed installed values. Aging, lining and condition can change resistance.

EPA new-pipe C-factor reference ranges
New pipe materialC range
Plastic140–150
Steel140–150
Cast iron130–140