HazenWilliams Coefficient
HazenWilliams coefficient, abbreviated as C, also called HazenWilliams friction coefficient or, HazenWilliams roughness coefficient, a dimensionless number, is used in the HazenWilliams Equation. The coefficient is used in fluid dynamics to calculate the resistance of water flow in a pipe network. 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.
The HazenWilliams coefficient represents the internal roughness of the pipe, taking into account factors such as pipe material, age, and condition. It is used to incorporate the effect of pipe roughness on the flow characteristics. The higher the coefficient, the smoother the pipe surface, resulting in a higher flow rate for a given pressure drop. The HazenWilliams coefficient varies depending on the pipe material, and it is typically determined through empirical testing. The coefficient values for different pipe materials are usually available in engineering references and design manuals.
It's important to note that the HazenWilliams equation is an empirical approximation and is most accurate for steady, uniform flow conditions in water supply systems. For more complex or nonuniform flow situations, other equations, such as the DarcyWeisbach equation, may be more appropriate.
Note that the HazenWilliams Coefficient is '''not''' the same as the DarcyWeibachColebrook friction factor, f. These are not in any way related to each other.
HazenWilliams coefficient formula 

\(\large{ C = \frac {v}{ 1.318 \; r_h^{0.63} \; m^{0.54} } }\) (mean flow velocity)  
Symbol  English  Metric 
\(\large{ C }\) = HazenWilliams Coefficient, see below for values  \(\large{ dimensionless }\)  
\(\large{ v }\) = mean flow velocity  \(\large{\frac{ft}{sec}}\)  \(\large{\frac{m}{s}}\) 
\(\large{ r_h }\) = hydraulic radius  \(\large{ ft }\)  \(\large{ m }\) 
\(\large{ m }\) = hydraulic grade line slope  \(\large{ dimensionless }\) 
HazenWilliams coefficient formula 

\(\large{ C = \frac {Q}{ 0.285 \; d^{2.63} \; m^{0.54} } }\) (fluid flow rate)  
Symbol  English  Metric 
\(\large{ C }\) = HazenWilliams Coefficient, see below for values  \(\large{ dimensionless }\)  
\(\large{ Q }\) = flow rate  \(\large{\frac{ft^3}{sec}}\)  \(\large{\frac{m^3}{s}}\) 
\(\large{ d }\) = pipe inside diameter  \(\large{ in }\)  \(\large{ mm }\) 
\(\large{ m }\) = hydraulic grade line slope  \(\large{ dimensionless }\) 
HazenWilliams Coefficient 

Material  Coefficient 
Aluminum  130  150 
Asbestos Cement  120  150 
Asphaltlined 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 
Lead  130 
Polyethylene  140 
PVC, PE, GRP  120  150 
Steel, new unlined  120 
Steel, 15 years  200 
Steel, riveted joints  95  110 
Steel, welded joints  100  140 
Steel, welded joints, lined  110  140 
Steel, welded or steamless  100  120 
Tin  130 
Wood Stave  110 
Tags: Coefficient Equations Pipe Sizing Equations HazenWilliams Equations