Calculation method and use
Evaluates water-pipe head loss, flow or diameter relationships with the empirical Hazen-Williams equation.
h_f ≈ 10.67 × L × Q^1.852 / (C^1.852 × D^4.87)
CivilCalc • Infrastructure / Water Supply
Hazen-Williams Calculator
Estimate head loss in pressurized water pipes from flow, diameter, length and Hazen-Williams C coefficient.
Hazen-WilliamsC coefficientHead lossPressure pipe
Unit System
Hazen–Williams Calculator
Calculate head loss, flow rate or approximate required inside diameter for pressurized water pipelines using the Hazen–Williams equation.
Velocity0.00 m/s
Head loss per km0.00 m/km
Total head loss0.00 mSS
Pressure drop0.00 bar
hf = 10,67 · L · Q1,852 / (C1,852 · D4,87)
Calculated flow0.00 L/s
Calculated flow0.00 m³/h
Velocity0.00 m/s
Head loss per km0.00 m/km
Theoretical inside diameter0,0 mm
Theoretical inside diameter0.000 m
Velocity at this diameter0.00 m/s
Check head loss0.00 m/km
The Hazen–Williams C coefficient varies with pipe material, age, lining and operating condition. Defaults are for preliminary estimates; use manufacturer/authority data and actual inside diameter for final design.
Example and practical interpretation
Points to check
- Choose C for the pipe material and condition.
- Confirm the unit system used by the equation.
- Include static head and local losses in full pumping calculations.
Frequently asked questions
What is Hazen-Williams C?
An empirical coefficient representing hydraulic smoothness of the pipe.
What fluid is Hazen-Williams commonly used for?
It is most commonly applied to water distribution and conveyance systems.
What happens when diameter increases?
For the same flow, friction head loss decreases strongly as diameter increases.
Hazen–Williams C Coefficient Reference
A higher C represents a hydraulically smoother pipe and produces lower calculated friction loss for the same flow and diameter. These ranges are useful for preliminary comparison; pipe age, lining condition and manufacturer or authority data should govern final design.
| Pipe / condition | Typical C | Design note |
|---|---|---|
| New PVC / HDPE / GRP | ≈ 140–150 | Smooth new internal surface |
| Cement-mortar-lined ductile iron | ≈ 130–140 | Verify lining condition |
| New steel | ≈ 120–140 | Internal coating matters |
| Concrete | ≈ 110–130 | Surface condition and age matter |
| Older steel / cast iron | ≈ 80–120 | Aging and deposits may increase loss |
C is not a permanent material constant. Select it for the actual internal condition and design life of the pipe.
How Strongly Does Pipe Diameter Affect Head Loss?
This comparison holds flow, length and C constant and changes only internal diameter. Because diameter appears with an exponent of about 4.87, a modest increase in diameter can sharply reduce friction head loss.
Diameter increase vs. friction head loss
4 in / 100 mm
196.3 ft / 59.85 m
5 in / 125 mm
66.2 ft / 20.19 m
6 in / 150 mm
27.3 ft / 8.31 m
8 in / 200 mm
6.7 ft / 2.05 m
10 in / 250 mm
2.3 ft / 0.69 m
Illustrative comparison at approximately 317 GPM (20 L/s), 3,281 ft (1,000 m) and C=140.
Worked Water-Main Example
Consider approximately 317 GPM (20 L/s) through a 6 in (150 mm) internal-diameter pipe over 3,281 ft (1,000 m), using C=140.
1. Flow = 317 GPM (20 L/s)
2. Inside diameter = 6 in (150 mm)
3. Friction head loss ≈ 27.3 ft (8.31 m)
4. Average velocity ≈ 3.7 ft/s (1.13 m/s)
2. Inside diameter = 6 in (150 mm)
3. Friction head loss ≈ 27.3 ft (8.31 m)
4. Average velocity ≈ 3.7 ft/s (1.13 m/s)
For pump-system head, add static elevation difference and applicable minor losses from valves, bends, tees and fittings rather than treating Hazen–Williams friction as the total dynamic head by itself.
How C Changes the Result
For the same flow, 6 in (150 mm) diameter and 3,281 ft (1,000 m) length, calculated friction loss rises as C falls: about 24.0 ft (7.31 m) at C=150, 27.3 ft (8.31 m) at C=140, 36.3 ft (11.05 m) at C=120 and 50.8 ft (15.49 m) at C=100. Using a new-pipe C for an aged line can therefore understate expected friction loss.
Engineering Checks After the Hazen–Williams Calculation
1. Actual inside diameter
Use the manufacturer's internal diameter rather than nominal pipe size.
Use the manufacturer's internal diameter rather than nominal pipe size.
2. Flow velocity
Check velocity against project and authority criteria.
Check velocity against project and authority criteria.
3. Static head
Do not confuse elevation difference with friction head loss.
Do not confuse elevation difference with friction head loss.
4. Minor losses
Evaluate valves, bends, tees and entrance/exit losses separately.
Evaluate valves, bends, tees and entrance/exit losses separately.
5. Operating cases
Check minimum, normal and peak-flow scenarios where relevant.
Check minimum, normal and peak-flow scenarios where relevant.
6. Method limits
For non-water fluids or cases where viscosity matters, consider the more general Darcy–Weisbach method.
For non-water fluids or cases where viscosity matters, consider the more general Darcy–Weisbach method.