Darcy Weisbach Equation

Solve for:
	Moody Friction Factor, f:
Select units:	Duct Length, L (ft):
	Duct Diameter, D (ft):
	Duct Area, A (ft²):
www.LMNOeng.com	Duct Perimeter, P (ft):
	Velocity, V (ft/s):
© LMNO Engineering,	Discharge, Q (ft³/s):
Research, and Software, Ltd.	Major Loss, h_f (ft):

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

Darcy-Weisbach Friction Loss Equation:

Major Loss Equations

If non-circular duct, D computed from D = 4A/P

D is called the "duct diameter" to keep the terminology general to include circular pipes and non-circular pipes, also known as ducts. For rectangular pipes (ducts), D=4A/P is known as the hydraulic diameter. More information about hydraulic diameter can be found on our non-circular to circular pipe conversion page.

g = acceleration due to gravity = 32.174 ft/s² = 9.806 m/s².

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 duct. It is also known as friction loss. The Darcy-Weisbach method is generally considered more accurate than the Hazen-Williams method. Additionally, the Darcy-Weisbach method is valid for any liquid or gas; Hazen-Williams is only valid for water at ordinary temperatures (40 to 75 ^oF). The Hazen-Williams method is very popular, especially among civil engineers, since its friction coefficient (C) is not a function of velocity or duct diameter. Hazen-Williams is simpler than Darcy-Weisbach for calculations where you are solving for flowrate, velocity, or diameter. More Discussion and References.

The Darcy-Weisbach calculation does not check for unreasonable inputs such as negative values. All values should be entered as positive.

LMNO Engineering, Research, and Software, Ltd.
7860 Angel Ridge Rd. Athens, Ohio 45701 USA Phone: (740) 707-2614
LMNO@LMNOeng.com https://www.LMNOeng.com