Hazen Williams Equation

The Hazen–Williams Equation is an empirical equation widely used in practice. It is especially applicable for smooth pipes of medium and large diameters and pipes that are not attacked by corrosion .

For calculating the velocity of flow in pressurized system, hazen william formula is frequetly used and is as below;


For circular conduits, the formula transforms to,


and, the discharge is given by,



Q = Discharge in cubic meter per hour,

d = diameter of pipe in mm,

V = velocity in mps,

r = hydraulic radius in m,

S = slope of hydraulic gradeline,

C = Hazen-Williams coefficient.


Coefficient Table

Hazen williams coefficient for different pipe materials are as below;

Conduit Material
Recommended Values for
New pipesDesign
Concrete (RCC & PSC) with socket and spigot joints150120
Asbestos cement150120
Plastic pipes150120
Cast iron130100
Steel, welded joints140100
Steel, welded joints lined with cement and bituminous enamel150120
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