Liters Per Minute Calculator
Convert flow rate to liters per minute, or measure it directly from a timed fill.
Reviewed by the ToolNestr Editorial Team — July 2026
How the liters per minute calculator works
Flow rate is stated in gallons per minute in the US and liters per minute in most other countries, so converting between them comes down to one fixed constant: one US gallon equals 3.78541 liters. Multiplying a GPM figure by that constant gives liters per minute directly, letting you compare a fixture, pump, or irrigation emitter rated in one unit against a spec or requirement given in the other.
When you don't have a GPM number to convert — say, checking an actual tap or shower's real-world flow — you can measure liters per minute directly the same way as the bucket method for GPM: time how long a container of known volume takes to fill, then divide the volume in liters by the fill time in seconds and multiply by 60 to scale up to a full minute.
This conversion is useful for comparing fixture efficiency across regions and standards. Modern water-efficient shower heads are commonly rated around 6 to 9.5 liters per minute, equivalent to about 1.6 to 2.5 GPM, while older, unrestricted fixtures can flow considerably more in either unit system.
The US gallon-to-liter conversion factor (3.78541) is the NIST-defined exact value; fixture flow-rate ranges reference EPA WaterSense specifications for water-efficient plumbing fixtures.
Choose a method
Convert a known GPM, or time a real fill.
Enter the numbers
GPM, or container size and seconds.
Read LPM
Plus GPM and liters per hour for reference.
The formula explained
GPM to LPM
LPM = GPM × 3.78541. 10 GPM: 10 × 3.78541 = 37.85 LPM.
Measured method
LPM = (liters ÷ seconds) × 60. A 10 L container in 25 s: (10÷25)×60 = 24 LPM.
Liters per hour
= LPM × 60. At 24 LPM: 24 × 60 = 1,440 L/hr.
Worked example
A pump rated at 25 GPM, converted to metric.
Use cases for the LPM calculator
Checking shower and faucet efficiency
Time a bucket fill from your shower head and compare the result to water-efficient benchmarks to see whether an aerator or low-flow fixture would meaningfully cut water use.
Sizing irrigation and drip systems
Drip emitters and sprinkler heads are frequently rated in liters per hour or LPM outside the US, so converting a GPM pump spec to metric helps you match components correctly.
Comparing pump and pool equipment specs
Pool pumps, sump pumps, and well pumps are often rated in GPM in the US but LPM elsewhere, so converting lets you compare products from different markets on equal footing.
Lab and process flow verification
The timed-fill method gives a quick, low-tech way to verify an actual measured flow rate against a rated or expected specification without needing a flow meter.
Real-world context
A water-efficient shower head rated at 1.6 GPM is a common EPA WaterSense benchmark. Converting to metric: 1.6 × 3.78541 = 6.06 liters per minute, or 363.4 liters per hour if run continuously. This is the kind of number a homeowner comparing a US-rated fixture against a European or Australian metric flow-rate requirement would need, since plumbing codes and fixture ratings outside the US are almost always expressed in LPM rather than GPM.
A standard kitchen faucet rated at 5 GPM converts to 5 × 3.78541 = 18.93 liters per minute, or about 1,136 liters per hour. That is roughly three times the flow of the water-efficient shower head above, which illustrates why kitchen faucets are a bigger target for flow restrictors than shower heads when a household is trying to cut water use — the baseline flow rate is already several times higher.
The timed-fill method is useful when you don't trust a fixture's printed rating. Filling a 4-liter container from a hose bib in 20 seconds gives (4 ÷ 20) × 60 = 12 liters per minute, equivalent to about 3.17 GPM. Measuring directly like this is especially useful for older fixtures with no visible rating, or for verifying that a newly installed low-flow fixture is actually performing at its rated spec rather than running higher due to water pressure.
Common misconceptions
"A gallon is a gallon everywhere, so the conversion factor never changes." Not quite — there are different gallons. This calculator uses the US liquid gallon (3.78541 liters). The UK imperial gallon is larger, at about 4.54609 liters, so using the wrong gallon definition when converting a spec sheet from a British or Commonwealth source will introduce a meaningful error.
"Flow rate and water pressure are basically the same thing." They measure different quantities. Flow rate (LPM or GPM) is the volume moving past a point per unit time, while pressure (measured in PSI or bar) is the force pushing the water. A fixture can have high pressure but low flow if it's restricted, or high flow at relatively low pressure through a wide-open pipe.
Related calculators
Frequently asked questions
How do I convert GPM to liters per minute?
Multiply gallons per minute by 3.78541 to get liters per minute, since one US gallon equals 3.78541 liters. A flow of 10 GPM equals 10 × 3.78541 = 37.85 liters per minute.
How do I measure liters per minute directly?
Time how long it takes to fill a container of known volume (in liters), then divide the volume by the time in seconds and multiply by 60. A 10-liter container filling in 25 seconds: (10 ÷ 25) × 60 = 24 liters per minute.
What is a typical LPM for a shower head?
Modern water-efficient shower heads are often rated around 6 to 9.5 liters per minute (about 1.6 to 2.5 GPM), while older or unrestricted shower heads can flow considerably more, sometimes over 15 liters per minute.
Why convert between GPM and LPM?
Plumbing fixtures, pumps, and irrigation equipment are rated in GPM in the US and LPM in most other countries, so converting lets you compare a product spec sheet in one unit against a requirement given in the other.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.