Hazen-Williams Eq. Description Solve Equation Pd = f(Q,C,D) Q = f(Pd,C,D) C = f(Pd,Q,D) D = f(Pd,Q,C) Related Tools Darcy Units Conversion

# Hazen-Williams Equation

The Hazen-Williams equation for calculating the pressure drop due to friction for a given pipe diameter and flow rate is as follow

### The equation in SI units where
• P = frictional pressire drop, kPa/m
• Q = flow rate, m^3/h
• D = pipe inside diameter, mm
• C = Hazen-Williams C factor, dimensionaless

• In general an average value of C=100 is used for most applications.
The Hazen-Williams C factor depends on the type of the pipe material and the internal condition of the pipe. A low value such as C=75 may be used for pipe that is 10 to 15 yeas old

### The equation in U.S. customary units where
• P = pressure loss due to friction, psi per ft of pipe length
• Q = flow rate, gal/min
• D = pipe inside diameter, in
• C = Hazen-Williams roughness coefficient factor, dimensionaless

• Hazen-Williams C Factor Table
 Pipe material C factor Smooth pipes (all metal) 130-140 Cast iron (old) 100 Cast iron (unlined new) 120 Iron (worn/pitted) 60-80 Polyvinyl chloride 150 Brick 100 Smooth wood 120 Smooth masonry 120 Vitrified clay 110 Plastic 150