Plumbing
Plumbing Water Flow Calculator
How much water a pipe can carry at a given size and velocity, in GPM and litres per minute.
Result
This is the pipe's capacity at that velocity, not what a system will actually deliver. Available pressure, friction along the run, fittings, valves and the fixture itself all reduce it.
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About this calculator
What velocity is reasonable?
Five to eight feet per second for cold water. Higher gets noisy and erodes copper; lower needs pipe that is larger and more expensive than it has to be.
Where does 448.8 come from?
One cubic foot per second is 448.8 gallons per minute. It is the conversion that turns an area in square feet and a velocity in feet per second into GPM.
The formula
GPM = pipe area in square feet x velocity in ft/s x 448.8
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