Water Pipe Sizing Calculation Example – Part 1: Overview

This water piping system design calculation example will use the Darcy-Weisbach equation to calculate the pressure loss in a pipe and using that value it will check the appropriateness of the assumed pipe size.

Problem Definition









Fig.1:Water Pipe Sizing Design Calculation Schematic










Refer the above schematics (Fig.1) and observe the following inputs:

Total pipe length=7 meters

Pressure head=5 meters

Number of ball valves=2

Number of Tee bend=1

Also assume that the required flow rate at the pipe end is 0.5 liter/sec.

Find out the appropriate pipe size


Following stepwise procedure needs to be followed for finding out the appropriate pipe size of this water pipe sizing calculation example:

Step-1: Assume the pipe diameter as 20 mm.

Step-2: Determine the Effective Pipe Length

Step-3: Determine the Permissible Pressure Loss

Step-4: Determine Hydraulic Diameter of the pipe

Step-5: Determine the Relative Roughness of the pipe

Step-6: Determine the Reynolds Number

Step-7: Determine the Moody friction factor using Moody diagram

Step-8: Determine the Actual Pressure Drop in the Pipe using Darcy-Weisbach equation and check if it is below the permissible pressure loss as calculated in step-3

In the next part (part-2) of this pipe size calculation series will discuss about calculating effective pipe length.


Shibashis is a mechanical design engineer by profession and writer/blogger by passion. He has worked in various design projects in automobile, power plant and heavy earth moving equipment domain since 2005.

In his spare time apart from maintaining this blog, he enjoy investing time building his first RC plane
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