Gal per Minute to Liters: Flow Rate Converter

This calculator converts a flow rate given in gallons per minute (GPM) to liters per minute (L/min) and also shows liters per second and liters per hour. You enter the flow rate in GPM, and the calculator returns the equivalent in liters per minute as the main result, with the other units as supporting values.

Formula

The conversion is straightforward: 1 US gallon = 3.785411784 liters exactly (by definition). Therefore, to convert a flow rate from gallons per minute to liters per minute, multiply by 3.785411784.

In symbols: 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 second, divide the result by 60. For liters per hour, multiply by 60.

Worked Example

Using the default value of 5 GPM:

1. Liters per minute = 5 × 3.785411784 = 18.92705892 L/min, rounded to 18.93 L/min.
2. Liters per second = 18.92705892 / 60 = 0.315450982 L/s, rounded to 0.315 L/s.
3. Liters per hour = 18.92705892 × 60 = 1135.6235352 L/h, rounded to 1136 L/h.

The calculator shows the same results for the default inputs.

Why the Conversion Factor Is Not a Round Number

The US gallon is defined as exactly 231 cubic inches. In metric, one inch is exactly 2.54 cm, so one cubic inch is exactly 16.387064 cm³ (or mL). Multiplying 231 by 16.387064 gives 3785.411784 cm³, which is 3.785411784 liters. That is why the factor has many decimal places – it comes from the inch-to-centimeter definition, not from a simple round number.

Note that this calculator uses the US liquid gallon. The UK (imperial) gallon is larger: 1 imperial gallon = 4.54609 liters. If you are working with imperial gallons, the conversion factor is different. Most pumps, plumbing fixtures, and industrial flow meters in the US use US gallons, but always check the label or manual.

How to Use the Result

The result tells you how many liters of fluid pass a point per minute at the given flow rate. This is useful for:

• Sizing a pump or filter for an aquarium or pond.
• Estimating how long it takes to fill a tank or pool.
• Comparing flow rates of different nozzles or hoses.
• Converting data from US equipment for use with metric specifications.

For example, if you have a pump rated at 10 GPM, it moves about 37.85 liters per minute. To fill a 1000-liter tank, it would take about 26.4 minutes (1000 / 37.85).

Common Mistakes and Unit Mix-Ups

• Using the wrong gallon: Imperial vs. US. The difference is about 20%, so mixing them up leads to large errors.
• Confusing gallons per minute with gallons per hour: Some equipment lists flow in GPH. Divide GPH by 60 to get GPM before converting.
• Forgetting to convert time units: The factor 3.785 converts gallons to liters, but if you need liters per second, you must also divide by 60.
• Rounding too early: If you round 3.785 to 3.8, you introduce about 0.4% error. For most practical purposes that’s fine, but for precise work use the full factor.

Limits of the Formula

This conversion is purely a unit change – it does not account for temperature, pressure, or fluid type. A gallon of water and a gallon of oil have the same volume, so the flow rate in L/min is the same for the same GPM. However, the mass flow rate (kg/min) would differ because density differs. If you need mass flow, multiply the volumetric flow by the fluid’s density.

Also, the conversion assumes the gallon is the US liquid gallon. For dry gallons (used for some agricultural commodities) the factor is different, but that is rarely used for flow rates.

Frequently Asked Questions

How many liters per minute is 1 GPM?

1 US gallon per minute equals 3.785411784 liters per minute. For quick mental math, many people use 3.785 or even 3.8, which is within 0.4% of the exact value.

Is GPM the same as L/min?

No. GPM measures volume in gallons per minute, while L/min measures volume in liters per minute. They are different units; the conversion factor is 3.785411784 (US gallons to liters).

How do I convert liters per minute to gallons per minute?

Divide the L/min value by 3.785411784. For example, 10 L/min ÷ 3.785411784 ≈ 2.64 GPM.

What is the difference between US and imperial gallons in this conversion?

The imperial gallon is about 4.54609 liters, so 1 imperial GPM equals 4.54609 L/min. That’s about 20% more than the US gallon. Always verify which gallon your equipment uses.

Can I use this for any liquid?

Yes, because the conversion is based on volume, not mass. One gallon of any liquid is still 3.785 liters. However, if you need mass flow (e.g., kg/min), you must multiply by the liquid’s density.

Why do some pumps list flow in GPH instead of GPM?

GPH (gallons per hour) is common for larger flows like pool pumps. To convert GPH to GPM, divide by 60. Then multiply by 3.785 to get L/min.

Related

• How to Calculate n Value (Sample Size)
• Convert GPM to Litres Per Minute
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in gpm | Flow rate | gal/min | 5 | 0
out lpm | Liters per minute | L/min | gpm * 3.785411784 | 2
out lps | Liters per second | L/s | gpm * 3.785411784 / 60 | 3
out lph | Liters per hour | L/h | gpm * 3.785411784 * 60 | 0