# Pipe Sizing Calculation – Part 5: Determining the Relative Roughness Using Table

This article will show the table for absolute roughness (different to coefficient of friction) of pipe surfaces of few commonly used materials. The absolute roughness is used in the relative roughness calculation and in the water piping system sizing design calculations through Darcy–Weisbach equation.

Absolute Roughness Value table for Different Pipe Materials:

 Pipe surface materials Absolute roughness value ( k in mm) Aluminum 0.0012 Brass 0.001 Cast iron 0.26 Copper 0.0015 Concrete 0.3-3 Cement 0.3 Drawn tube 0.0015 Galvanized iron 0.15 Plastic, PVC 0 – 0.0015 Steel 0.045

The water pipe sizing calculation example, we are dealing with, has galvanized iron (GI) tubes. From the above absolute surface roughness table we can see the value for GI pipe is 0.15.

Relative roughness is the ratio of the absolute roughness and hydraulic diameter.

For our home water tube sizing example,

The value of relative roughness  =absolute roughness / hydraulic diameter (refer part-4)

= 0.15/ 20 = 0.0075

In the next part (part-6), we will calculate the Reynolds number for the piping system.

 Aluminum 0.0012 Brass 0.001 Cast iron 0.26 Copper 0.0015 Concrete 0.3-3 Cement 0.3 Drawn tube 0.0015 Galvanized iron 0.15 Plastic, PVC 0 – 0.0015 Steel 0.045

### Shibashis Ghosh

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies.
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