How to Calculate the Velocity of Water Through Pipes

Updated March 23, 2017

Plumbers usually measure flow rates in terms of the volume of water that passes each minute. Convert this value to velocity using the pipe's size.

Multiply flow rate in gallons per minute by 0.408. For instance, if the flow rate is 50 gal / min:

50 * 0.408

\= 20.4

Square the pipe's diameter, in inches. For instance, if the pipe measures 4 inches across:

4 * 4

\= 16

Divide the answer to step 1 by the answer to step 2.

20.4 / 16

\= 1.275

This answer is the water velocity in feet per minute.

Things You'll Need

  • Calculator or computer
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About the Author

Ryan Menezes is a professional writer and blogger. He has a Bachelor of Science in journalism from Boston University and has written for the American Civil Liberties Union, the marketing firm InSegment and the project management service Assembla. He is also a member of Mensa and the American Parliamentary Debate Association.