Relative Roughness

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Relative Roughness

Relative roughness ( \(k\) ) (dimensionless number) of a pipe is a ratio of the surface roughness to the diameter of the pipe.

Since the relative roughness is a dimensionless number, both the absolute roughness and diameter must carry the same units.  The relative roughness is used with the Moody Diagram when solving for the friction factor of a system. 

Relative Roughness FORMULA

\( k = \frac {\epsilon} {D}\)


\(k\) = relative roughness

\(\epsilon\) = absolute roughness

\(D\) = diameter of the pipe

Relative Roughness CALCULATOR


Tags: Equations for Friction