# Gallons Per Minute Calculator (GPM)

URL: https://speedycalculator.com/calculators/construction/gpm/
Last updated: 2026-10-25

> The gallons per minute calculator finds a flow rate from the volume collected and the time it took – the bucket test – in GPM, litres per minute and gallons per hour, and how long it will take to fill a pool or tank.

## Inputs

- Volume collected (US gal, L, m³, ft³, UK gal)
- Time to fill it (s, min)
- Volume to fill (pool, tank) (US gal, L, m³, ft³, UK gal)

## Results

- Flow rate
- Time to fill target volume

## Formula

```
Flow = volume ÷ time
Time to fill = target volume ÷ flow
```

## Explanation

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

FieldWhat to enterVolume collectedUnits: US gal, L, m³, ft³, UK galTime to fill itUnits: s, minVolume 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)152022.513.33301037.58456.67605

## Worked 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.

## FAQ

**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.