Liters per Minute Calculator

The simplest way is a timed fill test. Put a container of known size under the fixture, open it fully, and time how long it takes to fill. Then divide the litres collected by the seconds it took and multiply by 60.

For example, if a 20-litre bucket fills in 40 seconds, that is 20 divided by 40 times 60, which is 30 litres per minute.

Run the test a few times and average the results for a reliable figure. If you measured in gallons or millilitres, convert to litres first — 1 US gallon is 3.785 litres and 1 millilitre is 0.001 litre — and if you timed in minutes, use that directly instead of multiplying by 60.

For a whole house, a flow of roughly 23 to 45 litres per minute at the main is generally comfortable, letting you run a couple of fixtures at once without a noticeable pressure drop. Below about 11 LPM feels weak, and above 45 is strong.

At the fixture, flow rates are lower and often capped by code: modern shower heads are limited to about 9.5 LPM, bathroom faucets to around 5.7 LPM, and kitchen faucets to about 8.3 LPM.

What counts as adequate depends on how many fixtures run together and your household’s habits. This calculator rates your measured flow and shows how many common fixtures it could supply at once.

A residential well or bore is often considered adequate at around 19 litres per minute of sustained yield, though many lenders and health authorities look for a minimum closer to 11 to 19 LPM. A strong source may produce 38 LPM or more.

The important figure is the sustained yield, not a brief burst. A quick bucket test measures the flow coming out of the pressure tank, which can read high because the tank is simply emptying; the source’s actual recovery rate may be lower once the tank draws down.

For well-yield decisions — sizing a pump, buying a property, or troubleshooting low water — have a licensed driller run a proper draw-down or yield test rather than relying on a short fixture test.

To go from litres per minute to litres per hour, multiply by 60, since there are 60 minutes in an hour. To get litres per day, multiply the LPM figure by 1,440, the number of minutes in a day.

So a flow of 20 LPM is 1,200 litres per hour and 28,800 litres per day if it ran continuously.

These larger figures are useful for sizing storage tanks, estimating irrigation volumes, or working out how long a continuous fill would take. This calculator shows litres per hour and per day automatically, along with other rates like US gallons per minute and cubic metres per hour.

Divide the tank’s capacity in litres by the flow rate in litres per minute. The result is the fill time in minutes.

For example, filling a 1,000-litre tank at 20 LPM takes 1,000 divided by 20, which is 50 minutes. A 5,000-litre tank at 40 LPM takes 125 minutes, or about 2 hours 5 minutes.

Keep in mind that flow can fall as a tank or pressure system draws down, so a real fill may take a little longer than the simple calculation suggests. This calculator works out the fill time for any tank, pool or container size you enter.

On a well or bore system, a short bucket test often reads higher than the source’s true sustained output. That is because the water is coming from the pressure tank, which stores a reserve and empties quickly, so for the first minute or two you are measuring the tank emptying, not the source producing.

As the tank draws down and the pump has to keep up on its own, the flow settles to the source’s actual recovery rate, which can be noticeably lower.

To gauge sustained yield, run the water for a longer period — many minutes — and measure the flow once it stabilizes, or have a driller perform a proper yield test. A short test is fine for a fixture’s flow, but not for judging a well.

LPM (litres per minute) measures flow — how much water moves past a point in a given time. Water pressure, measured in bar or kilopascals, measures the force pushing the water. They are related but not the same.

A system can have high pressure but low flow if the pipe or fixture is restrictive, or good flow at modest pressure through a wide, open line. Pressure drives flow, but the pipe size, fixtures, and restrictions determine how much flow a given pressure actually delivers.

This calculator measures flow (LPM) from a timed fill. To measure pressure you need a gauge on a tap or the main; most homes sit around 3 to 5 bar. Both matter for how a system performs.

A bucket-and-stopwatch test is accurate enough for most practical purposes, and it is how plumbers often check a fixture’s flow. The main sources of error are timing the start and stop, splashing or overfilling, and using a container whose true volume differs from its label.

To improve accuracy, use a larger container so the fill takes longer and timing errors matter less, start timing the instant water hits the container, and run the test three times and average. Open the fixture fully each time.

For a fixture or hose, this is reliable. For a well’s sustained yield or for pump sizing, a short test can mislead — use a longer draw-down test or a professional measurement instead.