Pipe Sizing Calculation – Part 4: Determining Hydraulic Diameter of the Pipe System

We will learn about hydraulic diameter calculation in this part of the water piping system design calculation.

What is Hydraulic Diameter of Pipe?

It is the equivalent diameter of a circular cross section pipe which produces same force kind of force balance as that of the non-circular cross sectional duct. It is calculated from the following equation:

Hydraulic Dia (Dh) = (4* duct cross sectional area)/ (Wetted perimeter of the duct)…………………….Eq.1

The Dh (also called as hydraulic mean diameter) is used in the Reynolds number calculation and in the Darcy–Weisbach equation.


For the water pipe sizing calculation example, we are dealing in this series,

the duct cross sectional area = π*D*D/4

the wetted perimeter of the duct = π*D

So, from the Eq.1,

Dh = D = 20 mm


D – Pipe diameter assumed in the Part-1


In the next part (Part-5), we will see how to calculate the relative roughness for the pipes.

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.
Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.

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