The Colebrook-White formula:


1/sqrt(f) = 1.14 – 2 log10 [e/D + 9.35/(Re x sqrt(f))]


f = friction factor


e = internal roughness of pipe


D = internal diameter of pipe


Re = Reynolds number


Friction factors for turbulent flow calculated by Pipe Flow Expert are based on the Colebrook-White formula.


The friction factor for Laminar flow is calculated from f = 64/Re