Flow Rate Calculator
Calculate water flow rate through a pipe.
How It Works
Flow (ft³/s) = π × (Diameter ÷ 2 ÷ 12)² × Velocity. GPM = Flow ÷ 0.002228.
Example
3/4 in pipe at 4 ft/s flows about 5.5 GPM.
Frequently Asked Questions
What is the flow in a typical home?
A 3/4 in main at typical velocity moves 5–10 GPM — enough for most fixtures.
Why use 0.002228?
It converts cubic feet per second to gallons per minute.
Does pipe length reduce flow?
Yes, friction over long runs reduces flow; this calculator assumes ideal short-run conditions.