# Hazen-Williams Coefficient

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

The following values are used in the Hazen-Williams Equation.  The lower the coefficient, the smoother the pipe is.  The higher the coefficient, the less fluid flow is restricted.  By using pipe materials with improved flow characteristics, energy costs for pumping can be reduced or smaller pipes can be used.

Note that the Hazen-Williams Coefficient (also called Hazen-Williams friction coefficient) is '''not''' the same as the Darcy-Weibach-Colebrook friction factor, f.  These are not in any way related to each other.

## Formulas that use Hazen-Williams Coefficient

 $$\large{ C = \frac {v}{ 1.318 \; r_h^{0.63} \; m^{0.54} } }$$ (mean flow velocity) $$\large{ C = \frac {Q}{ 0.285 \; d^{2.63} \; m^{0.54} } }$$ (fluid flow rate)

### Where:

$$\large{ C }$$ = Hazen-Williams Coefficient, see below for values

$$\large{ Q }$$ = flow rate

$$\large{ m }$$ = hydraulic grade line slope

$$\large{ r_h }$$ = hydraulic radius

$$\large{ v }$$ = mean flow velocity

$$\large{ d }$$ = pipe inside diameter

### Solve for mean flow velocity

 $$\large{ m = \left( \frac {v}{ 1.318 \; C \; r^{0.63} } \right) ^\frac{1}{0.54} }$$ $$\large{ r = \left( \frac {v}{ 1.318\; C \; m^{0.54} } \right) ^\frac{1}{0.63} }$$ $$\large{ v = 1.318 C \; r^{0.63} \; m^{0.54} }$$

### Solve for fluid flow rate

 $$\large{ m = \left( \frac {Q}{ 0.285 \; C \; d^{2.63} } \right) ^\frac{1}{0.54} }$$ $$\large{ d = \left( \frac {Q}{ 0.285 \; C \; m^{0.54} } \right) ^\frac{1}{2.63} }$$ $$\large{ Q = 0.285 \; d^{2.63} \; m^{0.54} }$$

## Hazen-Williams Coefficient Table

MaterialHazen Williams Coefficient
Aluminum 130 - 150
Asbestos Cement 120 - 150
Asphalt-lined iron or steel 140
Brass 130
Cast Iron, cement lined 140
Cast Iron, coated 110 - 140
Cast Iron, new unlined 130
Cast Iron, old unlined 40 - 120
Cast Iron, uncoated 100 - 140
Cast Iron, 10 years old 107 - 113
Cast Iron, 20 years old 89 - 100
Cast Iron, 30 years old 75 - 90
Cast Iron, 40 years old 64 - 83
Cement lining 140
Concrete 100 - 140
Concrete, old 100 - 110
Copper 130 - 140
Corrugated Metal Pipe 60
Corrugated Steel 60
Deteriorated old pipes 60 - 80
Ductile Iron 120 - 145
Fiberglass 150
Galvanized Iron 100 - 120
Glass 130