How to Calculate Pipe Pressure Loss

Updated April 17, 2017

Pressure drop in pipes is often due to friction loss. A standard residential system has two parts. The pump in the first part of the system has to make enough pressure for the water to reach the pressure tank. In the second part of the system, the pressure tank has to make enough pressure for the water to overcome friction loss and a vertical climb. Calculating pressure drop for the system is necessary to know how much pressure is needed to keep the water flowing properly.

Draw a diagram of the pipe system. Note the flow rate of water, diameter and length of all parts of the pipe system. To determine the flow rate, use your water meter to determine the gallons of water per minute (q) that flow through the pipe. Determine the velocity with the following calculation:

v = 0.4085 q/d2, where:

v = velocity (feet/second)

q = volume flow (gallons/minute)

d = pipe inside diameter (inches)

Then determine the flow rate with the following calculation for your pipe:

Q = VA, where:

Q = Flow rate

V = Velocity

A = Area (L^2)

Create a chart in table form with columns. Represent each pipe section in the vertical title of the chart. Represent the length, diameter and flow rate of each pipe section in the horizontal sections of the chart.

Use the pressure drop table located at to find the pressure loss for each section of the system.

Create a length and valve fittings table by using the example located at Add the lengths and valve fittings to find the total length for each section of the pipe system.

Add the pressure losses for all sections of the pipe system to determine the total pressure drop.


You can obtain a pipe layout diagram from your local water/sewer company.

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About the Author

Kim Sarah has been a writer since 2000. Her work has appeared on NECN, WCTR-TV3 and in the "Torch" university newspaper, among other publications. Sarah received a Bachelor of Arts in communications from Worcester State University and a Master of Arts in journalism from Roosevelt University. She is also studying nursing and computer science at Indiana State University.