Relative Roughness

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

relative roughness 1Relative roughness, abbreviated as k, a 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

\(\large{ k = \frac {\epsilon} {d} }\) 
Symbol English Metric
\(\large{ k }\) = relative roughness   \(\large{ dimensionless }\)
\(\large{ \epsilon }\)  (Greek symbol epsilon) = absolute roughness \(\large{ in }\) \(\large{ mm }\)
\(\large{ d }\) = pipe inside diameter \(\large{ in }\) \(\large{ mm }\)


Relative Roughness CALCULATOR


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Tags: Friction Equations Calculators