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Swamee-Jain equation

The Swamee-Jain equation is used to solve directly for the Darcy-Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook-White equation.

f =  \frac{0.25}{[log (\frac{\epsilon}{3.7D} + \frac{5.74}{Re^{0.9}})]^2}

Where f is a function of:

  • roughness height, ε (m, ft)
  • pipe diameter, D (m, ft)
  • Reynolds number, Re (unitless).

The equation was found to match the Colebrook-White equation within 1.0% for 10-6 < ε/D < 10-2 and 5000 < Re < 108.


  • Swamee, P.K.; Jain, A.K. (1976). "Explicit equations for pipe-flow problems". Journal of the Hydraulics Division, ASCE 102 (5): 657–664.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Swamee-Jain_equation". A list of authors is available in Wikipedia.
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