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Hazen-Williams Eq.
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  Pd = f(Q,C,D)    New Window
  Q = f(Pd,C,D)    New Window
  C = f(Pd,Q,D)    New Window
  D = f(Pd,Q,C)    New Window
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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

  • 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

  • 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 materialC factor
    Smooth pipes (all metal)130-140
    Cast iron (old)100
    Cast iron (unlined new)120
    Iron (worn/pitted)60-80
    Polyvinyl chloride150
    Smooth wood120
    Smooth masonry120
    Vitrified clay110


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