Flow Rate Converter: LPM to GPM, GPM to m³/h

LPM, GPM, and m³/h are all commonly used units of volumetric flow rate. They can be converted as follows: 1 L/min = 0.2642 US GPM, and 1 US GPM = 0.2271 m³/h. Different industrial product segments tend to prefer different units. For example, flow meters typically use LPM, while data sheets for U.S. pumps or valves prefer GPM, and projects in India or Southeast Asia often calculate flow rates in m³/h.

Therefore, we’re providing a simple Flow Rate Converter here, along with a detailed analysis of LPM, GPM, and m³/h.

RFQ

Flow Rate Converter

What is LPM

LPM stands for “Liter Per Minute,” which represents the volume of fluid flowing per minute. LPM is a metric unit commonly used in industries such as manufacturing, healthcare, laboratories, and water treatment. Examples include our diesel flow meters and gas metal rotor flow meters.

What is GPM

GPM stands for “Gallons Per Minute” and is a U.S. customary unit. In fact, there are two types of GPM: U.S. GPM and Imperial GPM. The two are not equivalent. Imperial GPM uses the imperial gallon (4.546 liters), which is approximately 20% larger than the U.S. unit.

However, US GPM is more widely used, particularly in North American engineering and HVAC industries, where GPM is the mainstream unit of flow. Therefore, unless otherwise specified, GPM in pump and flowmeter data sheets refers to US gallons (3.785 liters).

What is m³/h

m³/h stands for “cubic meters per hour” and represents the volume of fluid that passes through in one hour; it is a commonly used unit of volumetric flow rate. It is a metric unit. This is the most commonly used unit of volumetric flow rate in industrial processes: data sheets for electromagnetic flowmeters and vortex flowmeters almost exclusively use m³/h.

However, when used for gases, it is important to distinguish between m³/h (at operating conditions) and Nm³/h (at standard conditions), as these two units are not directly interchangeable.

LPM to GPM (and GPM to LPM)

The conversion relationship between LPM and GPM is: 1 LPM = 0.264172 US GPM, and 1 US GPM = 3.78541 LPM; when converting to Imperial GPM, 1 LPM = 0.219969 Imperial GPM.

Basic Conversion Formulas:

LPM → GPM (US): GPM = LPM × 0.264172

Example: 25 LPM = 25 × 0.264172 = 6.604 GPM

GPM (US) → LPM: LPM = GPM × 3.78541

LPM → GPM (UK): GPM = LPM × 0.219969

GPM (UK) → LPM: LPM = GPM × 4.54609

Common Conversion Table (US GPM)

GPM to m³/h (and m³/h to GPM)

The conversion relationship between GPM and m³/h is: 1 US GPM = 0.227125 m³/h, and 1 m³/h = 4.402868 US GPM. For Imperial GPM, 1 Imperial GPM = 0.272765 m³/h.

Basic Conversion Formula:

GPM (US) → m³/h: m³/h = GPM × 0.227125

Example: 250 GPM = 250 × 0.227125 = 56.78 m³/h

m³/h → GPM (US): GPM = m³/h × 4.402868

GPM (UK) → m³/h: m³/h = GPM × 0.272765

m³/h → GPM (UK): GPM = m³/h × 3.666154

Common Conversion Table (US GPM)

US Gallon vs Imperial Gallon: The 20% Trap

An imperial gallon is approximately 4.546 liters, while a US gallon is approximately 3.785 liters; the imperial gallon is about 20% larger than the US gallon.

Imperial gallon (UK gallon): Originated in the United Kingdom. One imperial gallon is defined as exactly 4.54609 liters.

U.S. gallon (US gallon / Liquid gallon): Widely used in the United States and some other countries; 1 U.S. gallon is approximately equal to 3.785411784 liters and is defined as 231 cubic inches.

The imperial gallon is about 20% larger than the U.S. gallon, so it is essential to distinguish between the two when converting or using them; otherwise, significant errors may occur. For example, 45 liters of liquid is approximately equal to 11.89 U.S. gallons, but only about 9.90 imperial gallons.

We recently received an inquiry from a Colombian customer regarding the measurement of solvent flow, with a requirement of 280 GPM, a 3″ pipe, and an accuracy of 0.2%.

First, convert the units: 280 US GPM × 0.227125 = 63.6 m³/h.

Based on the pipe diameter, a DN80 oval gear flowmeter would normally be selected. However, 63.6 m³/h exceeds the measuring range of a DN80 meter; selecting it would place the typical flow rate at the high end of the range or even beyond it. We ultimately quoted a DN100 model with a measurement range of 80–400 GPM (approximately 18–91 m³/h), where 280 GPM falls within the middle of the range.

This case illustrates that while the customer provided the flow rate in GPM and our catalog lists values in m³/h, after conversion, we must verify the actual flow rate against the catalog’s measurement range table—we cannot simply select a model based on pipe diameter alone.

Check the Flow Velocity

After converting the units, you must also calculate the flow velocity of this flow rate within the selected pipe diameter to confirm that it falls within the flowmeter’s measurement range. It is not sufficient to simply ensure that the flowmeter’s diameter matches that of the pipe.

For example, an electromagnetic flowmeter measures flow velocity, not flow rate. After converting to flow rate, you must calculate the flow velocity within the selected pipe diameter.

v = Q ÷ A (A = π × D² ÷ 4; Q is in m³/s, D is the inner diameter in meters)

Example: A pump data sheet lists 250 GPM, which converts to 56.8 m³/h.

The measurement range of an electromagnetic flowmeter is generally 0.3–10 m/s, and it is best to maintain a flow velocity within 2–3 m/s. For slurries, use a lower value; for media prone to scaling, do not allow the flow velocity to fall below 2 m/s. If the flow velocity remains below 0.5 m/s for an extended period, the meter can be installed with a reduced-diameter fitting, provided the taper angle of the reducer does not exceed 8°.

Normal flow should ideally be at or above 50% of full scale.

Flow Meters for Your Converted Flow Rate

Send us the medium, pipe size and flow range in any unit, and we will check the meter size against its velocity range.

Magnetic Flow Meters

For conductive liquids in water, slurry and chemical lines. DN2–DN3000, PTFE liner, 0.5% accuracy, 4-20mA and RS485 output.

SI-3603 Stainless Steel Oval Gear Flow Meter

For oils, solvents and corrosive liquids. DN10–DN200, class 0.5 or 0.2, up to 280 °C, pulse and 4-20mA output.

SI-3202 Liquid Turbine Flow Meter

For water, oil, fuel and chemicals. DN4–DN200, 0.5% accuracy (0.2% optional), pulse, 4-20mA or RS485 output.

FAQ

Can you convert LPM to PSI?

No, LPM is a unit of volumetric flow rate, while PSI is a unit of pressure. These two describe completely different parameters and cannot be converted. Of course, they often appear together in pipe flow measurement; our pipe flow vs. pressure calculator illustrates the relationship.

How many liters are in a UK gallon?

1 Imperial gallon is exactly equal to 4.54609 liters.

Is m³/h the same as CFM?

No, they are not the same. Both are units of volumetric flow rate, but 1 m³/h = 0.5886 CFM, while 1 CFM = 1.699 m³/h. For gas flow rates under standard conditions, please refer to our “SCFM and ACFM Calculator.”

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Zhang Wei

Zhang Wei, possesses 20 years of experience as an automation instrumentation engineer, specializing in the research, design, installation, commissioning, and maintenance of automation instruments.

Face to various instrument communication protocols (such as Modbus, Profibus, etc.), with solid hardware circuit design and software programming skills (proficient in C language and PLC programming). Has extensive project experience; projects he has led and participated in have all achieved outstanding results, improving product accuracy, reducing costs, and increasing production efficiency.

Possesses excellent communication and coordination skills and a strong team spirit, enabling him to quickly respond to customer needs and provide high-quality automation instrumentation solutions.