Absolute roughness

Absolute Roughness (k) is a measure of pipe wall irregularities. The absolute roughness has dimensions of length and is usually expressed in millimeter (mm) or feet (ft). Absolute Roughness is usually defined for a material and can be measured experimentally. Absolute roughness is important when calculating pressure drop particularly in the turbulent flow regime.

For each pipe material either a single pipe roughness value or a range of roughness values is normally provided by the manufacturer. The roughness value, usually denoted as e or k, is used in the calculating the relative roughness of a pipe against the size of its diameter.