GPM to Liters Per Minute Converter

This calculator converts a flow rate given in gallons per minute (GPM) to liters per minute (L/min). You enter the value in GPM, and the calculator returns the equivalent flow rate in liters per minute, along with the result in liters per hour for convenience. The conversion uses the standard US liquid gallon definition.

Formula

The conversion factor between US gallons and liters is exact: 1 US gallon = 3.785411784 liters. Therefore, the formula is:

L/min = GPM × 3.785411784

Where:

• GPM = flow rate in US gallons per minute
• L/min = flow rate in liters per minute

For liters per hour, multiply the result by 60 (minutes per hour): L/h = GPM × 227.12470704.

Worked Example

Using the default value of 10 GPM:

1. Start with the flow rate: 10 GPM
2. Multiply by the conversion factor: 10 × 3.785411784 = 37.85411784 L/min
3. Round to two decimal places: 37.85 L/min
4. For liters per hour: 37.85411784 × 60 = 2271.2470704 L/h, rounded to one decimal: 2271.2 L/h

So 10 GPM equals 37.85 liters per minute, which is about 2271 liters per hour.

Why Convert GPM to L/min?

Gallons per minute is the standard flow unit in the United States for plumbing, irrigation, pool pumps, and many industrial pumps. Most of the rest of the world uses liters per minute or cubic meters per hour. If you are sizing a pump, selecting a filter, or comparing equipment from different countries, you will often need to convert between these units. For example, a European pump datasheet might list capacity in L/min, while your US-based system spec is in GPM. This converter lets you compare them directly.

How the Conversion Works

The conversion relies on the definition of the US liquid gallon, which is exactly 231 cubic inches. In metric terms, 1 US gallon = 3.785411784 liters (this is an exact definition, not a rounded approximation). To convert a flow rate, you multiply the number of gallons by this factor. Because flow rate is a volume per time, the time unit (minutes) stays the same. If you need liters per second, divide the L/min result by 60. If you need cubic meters per hour (m³/h), divide the L/min result by 1000 and multiply by 60.

Common Mistakes and Unit Mix-Ups

The most frequent error is using the UK (imperial) gallon instead of the US gallon. The imperial gallon is about 20% larger: 1 imperial gallon = 4.54609 liters. If you accidentally use that factor, your result will be off by roughly 20%. Always confirm which gallon your source uses. Another common mistake is mixing up minutes and hours. If you convert GPM to liters per hour, remember to multiply by 60. A third issue is rounding too early. Use the full conversion factor (3.785411784) and round only at the end to avoid small errors that can accumulate in multi-step calculations.

When to Use This Converter

• Plumbing and irrigation: Sizing pipes, pumps, and sprinkler heads.
• Aquarium and pool equipment: Comparing pump flow ratings from different regions.
• Industrial processes: Reading flowmeter readings or pump curves.
• Automotive and machinery: Fuel pumps, coolant pumps, or hydraulic systems.
• Education: Converting units in physics or engineering homework.

For most practical purposes, the result to two decimal places is sufficient. If you are working on a high-precision application (like dosing chemicals), keep more decimal places and use the exact factor.

Limitations and Accuracy

This converter assumes a constant flow rate. Real systems may have pulsating flow (e.g., from a reciprocating pump) or varying flow due to pressure changes. The conversion is purely mathematical and does not account for temperature, viscosity, or pressure. For liquids other than water, the volume flow rate is still correct, but mass flow rate (kg/min) would require knowing the fluid density. Also note that the US gallon is used; if your source states “imperial gallon” or “UK gallon,” the conversion factor is different (4.54609 L/gal).

Frequently Asked Questions

Is 1 GPM equal to 3.79 L/min?

Yes, exactly 1 US GPM = 3.785411784 L/min. Rounded to two decimals, that is 3.79 L/min. This is the standard conversion factor used in most engineering and plumbing applications.

How do I convert L/min back to GPM?

Divide the number of liters per minute by 3.785411784. For example, 20 L/min ÷ 3.785411784 = 5.28 GPM. You can also multiply by 0.2641720524 (which is 1/3.785411784).

What is the difference between US and UK gallons?

The US liquid gallon is 231 cubic inches (3.785411784 L). The UK (imperial) gallon is 277.42 cubic inches (4.54609 L). The imperial gallon is about 20% larger. When converting, always verify which gallon is being used; most flow rates in the US are US gallons, while the UK and many other countries use liters directly.

How many liters per minute is 5 GPM?

5 GPM × 3.785411784 = 18.927 L/min. Rounded to two decimals, that is 18.93 L/min. This is a common flow rate for residential well pumps and small irrigation systems.

Can I use this for water flow in a pipe?

Yes, this conversion works for any liquid. The volume flow rate in GPM or L/min is independent of the fluid type. However, if you need to know the velocity in the pipe, you also need the pipe’s internal diameter. The flow rate alone does not tell you the speed.

What is a typical GPM for a household shower?

In the US, a standard showerhead flows at about 2.5 GPM (9.5 L/min). Low-flow models use about 1.5 GPM (5.7 L/min). This converter helps you compare those ratings with European showerheads, which are often labeled in L/min.

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in gpm | Flow rate (GPM) | gal/min | 10 | 0
out lpm | Flow rate (L/min) | L/min | gpm * 3.785411784 | 2
out lph | Flow rate (L/h) | L/h | gpm * 227.12470704 | 1