Hazen-Williams Head Loss Calculator
Head loss, pressure drop and velocity in a water pipe from flow rate, diameter, length and the C roughness coefficient.
Results
What this tool does
Water mains, sprinkler systems and irrigation lines are almost always sized with Hazen-Williams, because a single coefficient C covers the pipe material: around 150 for new plastic, 130 for cement-lined ductile iron, 100 for old steel that has been in the ground for decades. The formula is empirical and only valid for water, but within that world it is quick and it is what the codes expect.
Formula
hf = 10.67 L Q^1.852 / (C^1.852 D^4.8704)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
qq | Flow rate | L/s |
dd | Pipe diameter | mm |
ll | Pipe length | m |
cc | Hazen-Williams C | — |
HF | Head loss | m |
H1 | Head loss per 100 m | m |
VV | Speed | m/s |
DP | Differential pressure | bar |
Worked example
- Flow rate10 L/s
- Pipe diameter100 mm
- Pipe length50 m
- Hazen-Williams C130
- Head loss0.952 m
- Head loss per 100 m1.903 m
- Speed1.273 m/s
- Differential pressure0.0933 bar
Limitations
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
Frequently asked questions
When should I use Hazen-Williams instead of Darcy-Weisbach?
Hazen-Williams is an empirical formula fitted to water at ordinary temperatures in full pipes. It is quick because the C factor rolls roughness and viscosity into one number, and it is what most water-supply and irrigation codes use. For any other fluid, for hot water, or for gases, Darcy-Weisbach is the one that still holds.