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GPM to Litres Per Minute Conversion

Updated · Standard formula, shown below

Flow rate 37.85 L/min
Flow rate
10 GPM
You entered

This calculator converts a flow rate from gallons per minute (GPM) to litres per minute (L/min). You enter the flow rate in GPM, and the calculator returns the equivalent value in litres per minute, using the standard conversion factor of 1 US gallon = 3.785411784 litres.

Formula

The conversion uses a single multiplication step:

L/min = GPM × 3.785411784

Where:

  • GPM = flow rate in US gallons per minute
  • L/min = flow rate in litres per minute
  • 3.785411784 = exact number of litres in one US gallon

This factor is defined by international agreement. One US liquid gallon is exactly 231 cubic inches, and one litre is exactly 1,000 cubic centimetres. When you convert between the two, the factor above is exact, not an approximation.

Worked Example

Suppose you have a pump rated at 10 GPM. To find the flow in litres per minute:

  1. Start with the flow rate: 10 GPM
  2. Multiply by the conversion factor: 10 × 3.785411784
  3. Result: 37.85411784 L/min
  4. Rounded to two decimal places: 37.85 L/min

So a 10 GPM pump delivers about 37.85 litres every minute.

Why the Conversion Matters

Flow rate is a critical measurement in plumbing, irrigation, water treatment, and industrial processes. In the United States, flow rates are often given in GPM, while most other countries use litres per minute or cubic metres per hour. If you are importing equipment, reading a foreign manual, or comparing pumps from different manufacturers, you need a reliable conversion to avoid under- or over-sizing your system.

For example, a garden hose in the US might deliver 5–10 GPM, which is 19–38 L/min. A typical shower head in Europe is often rated at 6–12 L/min, which is about 1.6–3.2 GPM. Knowing the conversion helps you compare these directly.

US vs. Imperial Gallons

There are two different gallons in common use:

  • US liquid gallon = 3.785411784 litres (used in the US for most liquids)
  • Imperial gallon = 4.54609 litres (used in the UK, Canada, and some Caribbean countries for fuel and some other liquids)

This calculator uses the US gallon, which is the standard for most flow measurements in the US. If you are working with imperial gallons, the conversion factor is different: 1 imperial GPM = 4.54609 L/min. Always check which gallon your source uses before converting.

How to Read the Result

The result is the volume of liquid that passes a point in one minute. A higher L/min value means more flow. When you compare pumps or pipes, the flow rate tells you how quickly a tank fills or how much water a system can deliver.

For real-world context:

  • A small domestic pump might deliver 5 GPM (about 19 L/min)
  • A garden hose with good pressure can deliver 10 GPM (about 38 L/min)
  • A fire hose can deliver 100 GPM or more (about 379 L/min)

These examples show how the same number in GPM becomes a much larger number in L/min, simply because litres are smaller than gallons.

Common Mistakes and Unit Mix-Ups

The most frequent error is using the wrong gallon. If you use the imperial gallon factor on a US GPM value, you will overestimate the flow by about 20%. Always confirm the gallon type.

Another common mistake is confusing flow rate with volume. GPM and L/min are rates (volume per time), not total volumes. A pump that delivers 10 GPM for 5 minutes moves 50 gallons total, not 10 gallons. To convert total volume, you would multiply the flow rate by the time.

Also, be careful with rounding. The exact factor has many decimal places, but for most practical purposes, using 3.785 is accurate enough. However, if you are doing precise engineering calculations, use the full factor.

Alternatives and Related Conversions

If you need other flow units, here are common conversions:

  • 1 GPM = 0.06309 litres per second (L/s)
  • 1 GPM = 3.785 litres per minute (L/min)
  • 1 GPM = 0.2271 cubic metres per hour (m³/h)
  • 1 L/min = 0.2642 GPM

You can also convert between GPM and cubic feet per second (cfs) or barrels per day, but those are less common in everyday use. For most practical purposes, the GPM to L/min conversion is the one you need when working with pumps, pipes, and nozzles.

Frequently Asked Questions

Is 1 GPM equal to 3.785 L/min?
Yes, exactly. One US gallon is defined as 3.785411784 litres, so a flow of 1 gallon per minute is exactly 3.785411784 litres per minute. For quick estimates, you can use 3.8.

How do I convert L/min to GPM?
Divide the L/min value by 3.785411784. For example, 10 L/min ÷ 3.785411784 = 2.64 GPM. Many calculators also have a reverse button.

What is the difference between US and imperial GPM?
The US gallon is smaller (3.785 L) than the imperial gallon (4.546 L). So 1 imperial GPM is about 4.546 L/min, which is 20% more than 1 US GPM. Always check which gallon is being used.

Can I use this conversion for any liquid?
Yes, the conversion is purely a volume unit conversion. It does not depend on the liquid’s density, viscosity, or temperature. Whether it is water, oil, or any other fluid, 1 GPM always equals 3.785 L/min in volume.

Why do some countries use L/min instead of GPM?
Most countries use the metric system, where litres are the standard unit for volume. The US uses the customary system, which includes gallons. This calculator helps bridge the gap when working with international equipment or standards.

Related

Formula used
in gpm | Flow rate | GPM | 10 | 0
out lpm | Flow rate | L/min | gpm * 3.785411784 | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.