Darcy-Weisbach Pipe Friction Loss Calculator

Compute Major Losses (Friction Loss) in Pipes using Darcy-Weisbach Equation


Darcy-Weisbach calculation is mobile-device-friendly as of July 11, 2014

Solve for: 
Moody Friction Factor, f:  
Select units:  Duct Length, L (ft):  
Duct Diameter, D (ft):  
© 2014 LMNO Engineering, Duct Area, A (ft2):  
Research, and Software, Ltd. Duct Perimeter, P (ft):  
http://www.LMNOeng.com Velocity, V (ft/s):  
Discharge, Q (ft3/s):  
Major Loss, hf (ft):  

Units in Darcy-Weisbach calculator: ft=foot, m=meter, s=second.

Darcy-Weisbach Friction Loss Equation:

Major Loss Equations

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 (hf) 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.


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LMNO Engineering, Research, and Software, Ltd.
7860 Angel Ridge Rd.   Athens, Ohio 45701  USA   Phone and fax: (740) 592-1890
LMNO@LMNOeng.com    http://www.LMNOeng.com

August 25, 2015: Made text fields show 8 significant figures rather than 16. Calculation still uses double precision internally.


LMNO Engineering home page (more calculations)  

Pipe Design (Darcy-Weisbach friction losses)

Moody friction factor

Unit Conversions

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Discussion and References