Pipe Friction Loss Calculator

Work out pipe friction loss instantly with clear inputs, formula shown and shareable results.

About Pipe Friction Loss Calculator

The Hazen-Williams equation gives head loss for water in full pipes: hf = 10.67 L Q^1.852 / (C^1.852 D^4.87) in SI units. Because diameter appears to the 4.87 power, going up one pipe size cuts the loss dramatically, which is why oversizing a long main usually pays for itself in pumping energy.

Formulas

Hazen-Williams

hf = 10.67 L Q^1.852 / (C^1.852 D^4.87)

C: 150 plastic, 130 new steel or cement lined, 100 old steel

Pressure

kPa = head loss m x 9.807

Worked example

With the default values below, Pipe Friction Loss Calculator returns Head loss over the run of 0.527. Change any input above and every figure here is recalculated in your browser.

Inputs used

Flow rateminimum 0.01 L/s: 5 L/s
Internal diameterminimum 5 mm: 100 mm
Pipe lengthminimum 0.1 m: 100 m
Hazen-Williams C factorminimum 40: 130

Results

Head loss over the run: 0.527 m
Head loss per 100 metres: 0.527 m
Velocity: 0.637 m/s
Pressure loss: 5.17 kPa

Step by step

1Values used
2Hazen-Williams
3Pressure
4Head loss over the run= 0.527 m
5Head loss per 100 metres= 0.527 m
6Velocity= 0.637 m/s
7Pressure loss= 5.17 kPa

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Pipe Friction Loss figure worked out?

hf = 10.67 L Q^1.852 / (C^1.852 D^4.87). The Hazen-Williams equation gives head loss for water in full pipes: hf = 10.67 L Q^1.852 / (C^1.852 D^4.87) in SI units.

When should Darcy-Weisbach be used instead?

For anything other than water near room temperature, or where the flow may be laminar. Hazen-Williams is an empirical water-only fit and drifts outside its calibration range.

What values do I need to enter?

This calculator takes 4 inputs: Flow rate, Internal diameter, Pipe length, Hazen-Williams C factor. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.