Find a flow rate in gallons per minute (GPM) — the standard way pump, faucet, and irrigation output is measured.
How it works
GPM is the volume delivered divided by the time it took: GPM = Gallons ÷ Minutes. 500 gallons delivered over 25 minutes is a flow rate of 20 GPM.
What this does not include
This calculates an average flow rate from a measured volume and time — it doesn’t model how pipe diameter, pump pressure, or elevation change would affect flow rate in a system you haven’t measured directly.
How to use this calculator
- Enter the volume delivered, in gallons.
- Enter the time it took, in minutes.
A worked example
500 gallons collected over 25 minutes: flow rate = 500 ÷ 25 = 20 GPM.
1,200 gallons over 60 minutes: flow rate is also 20 GPM.
What the variables mean
| Variable | Meaning |
|---|---|
| Gallons | Total volume collected or delivered |
| Minutes | Time taken |
Edge cases worth knowing
The same GPM can come from very different total volumes and times, as both examples above show — flow rate is a ratio, not tied to any specific volume.
Zero minutes makes the flow rate undefined — no finite time means no meaningful rate to calculate, so the calculator declines to show a result.
Why does GPM matter for choosing a pump?
A pump’s GPM rating tells you how quickly it can move water, which determines whether it can keep up with a given irrigation zone, fill rate, or drainage need.
How is GPM different from PSI?
GPM measures volume over time (how much water moves); PSI measures pressure (how hard the water pushes) — a system can have high pressure and low flow, or the reverse.
How do I measure gallons and time to use this calculator?
Time how long it takes to fill a container of known volume (a 5-gallon bucket is a common choice), then enter that volume and time directly.
