Hazen-Williams Equation


Solve for:	Discharge, Q (ft³/s):
	Velocity, V (ft/s):
Select units:	Pipe Diameter, D (ft):
	Pipe Length, L (ft):
www.LMNOeng.com	Hazen-Williams C:
© LMNO Engineering,	Head Loss, h_f (ft):
Research, and Software, Ltd.	Energy Slope, S (ft/ft):

Units: ft=foot, m=meter, s=second.

Hazen-Williams Equation: V = k C (D/4)^0.63 S^0.54 where S = h_f / L and Q = V π D² / 4

k is a unit conversion factor:
k=1.318 for English units (feet and seconds). k=0.85 for SI units (meters and seconds)
C=Hazen-Williams Coefficient. D=Pipe inside diameter. π=3.14159...

Hazen-Williams Coefficient (C) varies from approximately C=60 for 40-year old cast iron pipe to C=150 for new plastic pipe. The higher the C, the smoother the pipe. Table of Hazen-Williams Coefficients.

The Hazen-Williams method is valid for water flowing at ordinary temperatures of 40 to 75 ^oF (4 to 25 ^oC) through pressurized pipes. The Hazen-Williams equation is typically used to analyze city water supply systems. For other liquids or gases, the Darcy-Weisbach method should be used. Major loss (h_f) is the energy (or head) loss (expressed in length units - think of it as energy per unit weight of fluid) due to friction between the moving fluid and the pipe wall. It is also known as friction loss. The Darcy-Weisbach method is generally considered more accurate than the Hazen-Williams method. However, the Hazen-Williams method is very popular, especially among civil engineers, since its friction coefficient (C) is not a function of velocity or pipe diameter. Hazen-Williams is simpler than Darcy-Weisbach for calculations where you are solving for flowrate (discharge), velocity, or diameter. More Discussion and References.

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