Liters per Minute Calculator

Time how long a tap, shower, hose or pump takes to fill a bucket and get the flow rate in L/min and gallons per minute, or convert a flow rate you already have between L/min, L/s, L/h, m³/h and US or UK gpm.

L/min = litres collected ÷ seconds × 60

Volume collected

Volume unit

Time to fill (seconds)

Running a Bucket Test You Can Trust

A bucket and a phone stopwatch are all you need, but a few habits decide whether the answer is within 2% or 20%:

Use a container that takes at least 20 seconds to fill. Your reaction time when starting and stopping the timer is around a quarter of a second. On a 5-second fill that's a 5% error; on a 40-second fill it's under 1%.
Get the flow steady first, then swing the bucket under it and start timing. Opening the tap with the bucket already in place undercounts.
Read the volume, don't assume it. A "10 L" bucket often holds 11–12 L to the rim. Fill to a marked line, or weigh it: each kilogram of water is about a litre.
Repeat three times and average. If the runs differ by more than a few percent, something else in the house was drawing water.
For a showerhead, hold a bin bag or bucket around the head so spray doesn't escape, then measure what you caught.

Worked Example: Checking an Old Showerhead

The water bill has crept up and you suspect the shower. You catch the spray in a bucket marked at 10 L, and it takes 48 seconds to reach the line. (This is the Load Example.)

Step 1: Litres per second

10 L ÷ 48 s = 0.2083 L/s

Step 2: Per minute

0.2083 × 60 = 12.5 L/min

Step 3: US gallons per minute

12.5 ÷ 3.7854 = 3.30 gpm

Step 4: Water used by an 8-minute shower

12.5 × 8 = 100 L, against 60.6 L at a 2.0 gpm (7.57 L/min) WaterSense head

At 12.5 L/min (3.3 gpm), the head is above the 2.5 gpm US limit that has applied to new showerheads since 1994. It's either older than that or has had its flow restrictor removed. Swapping to a 2.0 gpm head saves about 40 L per shower, and less hot water means a smaller energy bill too.

Flow Limits for Showers and Taps

These are maximums for new fixtures sold in the US, tested at a set pressure. Your measured flow can be lower if the house pressure is below the test pressure.

Maximum flow rates for showerheads and faucets in gpm and L/min
Fixture	Rule	gpm	L/min
Showerhead	US federal maximum (at 80 psi)	2.5	9.5
Showerhead	EPA WaterSense label	2	7.6
Showerhead	California (since July 2018)	1.8	6.8
Bathroom or kitchen faucet	US federal maximum (at 60 psi)	2.2	8.3
Bathroom faucet	EPA WaterSense label	1.5	5.7
Bathroom faucet	California	1.2	4.5

Flow Units and Where Each Is Used

Each field tends to pick the unit that gives it convenient numbers. A drip emitter at 0.033 L/min would be awkward, so it's sold as 2 L/h. A hydrant at 1,500 L/min reads better as 25 L/s.

Common flow rate units, their size in litres per minute and typical uses
Unit	= L/min	Typical use
Litres per hour (L/h)	0.0167	Drip emitters (2, 4 or 8 L/h), aquarium and fountain pumps
Litres per minute (L/min)	1	Taps, showers, garden hoses, small pumps, medical oxygen
Litres per second (L/s)	60	Fire hydrants and mains design in Europe and Australia
Cubic metres per hour (m³/h)	16.6667	Pump curves, circulators, pool filters, water meters
US gallons per minute (gpm)	3.7854	US plumbing fixtures, well pumps, tankless water heaters
UK gallons per minute	4.5461	Older British pump and boiler literature

"gpm" on its own means US gallons in almost every modern spec sheet. A UK gallon is 20% larger, so 10 UK gpm is 12 US gpm. For hydrant and nozzle flow worked out from pressure, see the PSI to GPM calculator.

How Long It Takes to Fill a Container

Fill time is volume ÷ flow rate. A garden hose on mains pressure typically gives somewhere between 15 and 40 L/min, so it's worth measuring yours before you plan to fill a pool overnight.

Time to fill common containers at 10, 20 and 40 litres per minute
Container	Volume	10 L/min	20 L/min	40 L/min
Watering can	10 L	1 min	30 s	15 s
Rain barrel or drum	200 L	20 min	10 min	5 min
IBC tote	1,000 L	1 h 40 min	50 min	25 min
Small above-ground pool	15,000 L	25 h 0 min	12 h 30 min	6 h 15 min

Oxygen and Other Gases in L/min

Oxygen concentrators, regulators and lab mass-flow controllers also show L/min, but a litre of gas changes size with pressure and temperature. Gas flow meters are calibrated to a reference condition, which is why lab equipment often says SLPM (standard litres per minute). A bucket test can't measure gas, and you shouldn't convert a gas reading to gpm.

Home oxygen by nasal cannula is usually prescribed somewhere around 1 to 5 L/min. The right setting is the one on your prescription; don't adjust it based on a calculator.

Frequently asked questions

How many L/min is 1 gpm?

1 US gallon per minute is 3.785 L/min, and 1 UK gallon per minute is 4.546 L/min. Going the other way, 1 L/min is 0.264 US gpm.

Why is my measured flow lower than the number on the box?

Fixture ratings are maximums at a test pressure (80 psi for showerheads, 60 psi for faucets). Pump ratings are usually the flow with nothing to push against. Real pipes, lifts and lower pressure all cut the flow.