By Zencalcy Editorial TeamLast reviewed About us
Flow rate is volume divided by time, but pumps are also rated by the velocity they produce in a pipe. Too slow and sediment settles; too fast and the pipe erodes and noisy. Residential plumbing typically targets 4–8 feet per second, and irrigation 5 fps or less.
Gallons per minute from a volume and a fill time.
GPM = gallons ÷ minutes Q = A × v
For the velocity mode, Q (gpm) = 2.448 × d² × v, with d in inches and v in feet per second. That constant comes from converting square inches and cubic feet to gallons per minute.
| Symbol | Meaning |
|---|---|
| V | Volume in gallons. |
| t | Time in minutes. |
| Q | Flow in gallons per minute. |
40 seconds is 0.667 minutes, so the flow is 7.5 gpm — 28.4 litres per minute.
Continue with the Pool Calculator, Round Pool Volume Calculator, Pond Calculator, or the Tank Volume Calculator — or browse more tanks, pools & flow and all construction calculators.
Fill a known container and time it. A 5-gallon bucket is ideal; run it for a full minute for a direct gpm reading.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026