The easiest way to measure the flow of a tap, hose, well pump or shower is a bucket test: time how long it takes to fill a container of known size. A typical garden hose delivers 9–17 gpm; a low-flow shower head is limited to 2.0 gpm in many U.S. states (1.8 in California).
How to use the Gallons Per Minute Calculator
- Volume collected
- Time to fill it
- Volume to fill (pool, tank)
- Every result field is editable: type into Flow rate and Time to fill it plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the container volume and the time to fill it. The calculator gives the flow rate in several units and the time to fill a larger volume such as a pool or tank.
Tips for an accurate estimate
- Measure inside dimensions of tanks and pools – wall thickness can change the volume noticeably.
- Use the average depth for pools with a sloping floor.
- Remember the weight: water weighs about 8.34 lb per US gallon (1 kg per litre), so large volumes need solid support.
- Check whether a figure is in US gallons, imperial gallons or litres before ordering chemicals or equipment.
Common mistakes to avoid
- Using wall height instead of water depth for above-ground pools.
- Assuming a horizontal tank’s volume is proportional to the liquid level – it is not.
- Mixing up flow units such as GPM, GPH and litres per minute.
Inputs explained
| Field | What to enter |
|---|---|
| Volume collected | Units: US gal, L, m³, ft³, UK gal |
| Time to fill it | Units: s, min |
| Volume to fill (pool, tank) | Units: US gal, L, m³, ft³, UK gal |
What each result means
- Flow rate = [Volume collected]÷[Time to fill it]
- Time to fill target volume = [Volume to fill (pool, tank)]÷[Flow rate]
Example values
How the main result changes when Time to fill it changes and everything else stays at the example values above:
| Time to fill it (s) | Flow rate (gpm) |
|---|---|
| 15 | 20 |
| 22.5 | 13.33 |
| 30 | 10 |
| 37.5 | 8 |
| 45 | 6.67 |
| 60 | 5 |
Formula
Flow = volume ÷ timeTime to fill = target volume ÷ flowWorked example
Inputs — Volume collected: 5 US gal; Time to fill it: 30 s; Volume to fill (pool, tank): 20,000 US gal.
Results — Flow rate = 10 gpm; Time to fill target volume = 33.33 h.
Frequently asked questions
How do I measure GPM?
Time how long it takes to fill a 5 gallon bucket; divide 5 by the seconds and multiply by 60.
What is a good water flow for a house?
6–12 gpm for a typical home; wells are often sized for 1 gpm per fixture.
How long does it take to fill a 20,000 gallon pool with a hose?
At 10 gpm, about 33 hours.
What formula does the Gallons Per Minute Calculator use?
Flow = volume ÷ time.