Convert GPM to Litres Per Minute

This calculator converts a flow rate given in US 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 exact conversion factor of 1 US gallon = 3.785411784 litres.

Formula

The conversion is a simple multiplication:

L/min = GPM × 3.785411784

Where:

• GPM = flow rate in US gallons per minute (gal/min)
• L/min = flow rate in litres per minute (L/min)
• 3.785411784 = exact number of litres in one US gallon (defined by international agreement)

Note: This uses the US liquid gallon. The UK (imperial) gallon is larger (4.54609 L), but in most industrial, automotive, and pump contexts, “gallon” refers to the US gallon. Always confirm which gallon your source uses.

Worked Example

Using the default value of 10 GPM:

1. Start with the flow rate: 10 gal/min.
2. Multiply by the conversion factor: 10 × 3.785411784 = 37.85411784 L/min.
3. Round to two decimal places: 37.85 L/min.

The calculator above gives 37.85 L/min for 10 GPM, matching this result.

Why Convert Between GPM and L/min?

Flow rate units vary by region and industry. GPM is common in the United States for plumbing, pool pumps, irrigation, and well pumps. Litres per minute is the standard in most other countries and in scientific contexts. If you are importing equipment, reading a spec sheet, or comparing pumps from different manufacturers, you will often need to convert between the two. For example, a European pump rated at 40 L/min is roughly 10.6 GPM—a useful number when sizing a filter or a water feature.

Another common scenario is converting a municipal water supply spec (often given in GPM) to what a household appliance expects (often in L/min). A standard garden hose in the US might deliver 5–10 GPM; in Europe, the same hose might be rated at 20–40 L/min. Knowing the conversion helps you choose the right nozzle or pump.

How to Read the Result

The result is a direct equivalence: if a pump moves 10 US gallons in one minute, it moves 37.85 litres in that same minute. The number does not depend on the fluid—water, oil, or any liquid—because the conversion is purely volumetric. However, if you are dealing with mass flow (kg/min), you would also need the fluid density.

When reading a pump curve or a spec sheet, check whether the manufacturer quotes GPM at a specific pressure (e.g., at 50 psi). The conversion factor stays the same, but the actual flow rate at your system’s pressure will differ. The calculator only converts units; it does not predict how a pump behaves under load.

Common Mistakes and Misconceptions

• Using the wrong gallon: The UK imperial gallon is 4.54609 L, about 20% larger than the US gallon. Mixing them up can cause significant errors in sizing.
• Confusing GPM with gallons per hour (GPH): If your source gives GPH, divide by 60 to get GPM before converting.
• Rounding too early: If you round the conversion factor to 3.78, you get a slightly different answer. For most practical purposes, 3.785 is enough, but for precise engineering, use the full factor.
• Assuming 1 L/min = 1 GPM: They are not equal; 1 GPM is about 3.785 L/min. A quick mental check: 4 GPM is roughly 15 L/min.

When to Use This Conversion

Use this calculator when you need to:

• Compare pump specifications from US and metric sources.
• Size a filter, heater, or chiller for an aquarium or pool (flow rates are often quoted in GPM in the US, L/min elsewhere).
• Convert a water softener or reverse osmosis system’s rated flow.
• Check if a well pump meets your household demand (e.g., a 10 GPM pump is about 37.85 L/min).
• Translate irrigation drip line or sprinkler specs.

The conversion is also useful in automotive cooling systems, where coolant flow is sometimes given in GPM, and in hydraulic systems, where metric pumps are rated in L/min.

Limits of the Formula

The conversion is exact and applies to any liquid at any temperature, as long as you are measuring volume flow. It does not account for:

• Viscosity: A pump’s actual output may vary with fluid viscosity, but the unit conversion remains the same.
• Pressure effects: Flow rate changes with pressure, but the conversion factor does not.
• Temperature: Volume changes slightly with temperature, but for most practical purposes, the difference is negligible.

If you need mass flow (e.g., kg/min), multiply the L/min by the fluid density in kg/L. For water at room temperature, density is about 1 kg/L, so 37.85 L/min is roughly 37.85 kg/min.

Frequently Asked Questions

Is 1 GPM equal to 3.785 L/min?

Yes, exactly. One US gallon is defined as 3.785411784 litres, so 1 GPM = 3.785411784 L/min. For quick estimates, use 3.8.

How do I convert L/min to GPM?

Divide the L/min value by 3.785411784. For example, 20 L/min ÷ 3.785411784 = 5.28 GPM.

What is the difference between US and UK gallons?

The US liquid gallon is 3.785411784 litres, while the UK (imperial) gallon is 4.54609 litres. The UK gallon is about 20% larger. Most modern usage in the UK and Europe is metric, but older documents may use imperial gallons.

Can I use this for any liquid?

Yes, because the conversion is purely volumetric. It does not matter whether the fluid is water, oil, or milk. However, if you need mass flow, you must also know the density.

Why do some pump specs use GPM and others L/min?

It depends on the manufacturer’s country and target market. US-based companies typically use GPM, while European and Asian companies use L/min. When comparing pumps, always convert to the same unit.

What is a typical household water flow rate?

A typical US home has a main line flow of 6–12 GPM (about 23–45 L/min). A shower uses about 2.5 GPM (9.5 L/min), and a garden hose about 5–10 GPM (19–38 L/min). These figures help when sizing a pump or a filter.

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in gpm | Flow rate (GPM) | US gal/min | 10 | 0
out lpm | Flow rate (L/min) | L/min | gpm * 3.785411784 | 2