US gallons per minute to liters per minute

An American shower head is legally capped at 2.5 gallons per minute — 9.46 liters per minute in any metric plumbing code. The conversion runs through 3.785411784, the exact liter content of the US gallon, and it is the most common pump-rating translation in the plumbing world: American pump curves say GPM, the rest of the world says L/min, and the same pump gets rated both ways.

1 US gallon per minute = 3.785411784 liters per minute, and 1 liter per minute = 0.264172 US gallons per minute. The conversion is a single fixed factor: multiply US gal/min by 3.785411784. Worked: 10 US gal/min = 37.85411784 L/min; 100 US gal/min = 378.5411784 L/min.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
US gallons per minute
18.92705892 liters per minute
5 US gallons per minute = 18.92705892 liters per minute 5 liters per minute = 1.32086026 US gallons per minute

Constants verified against NIST Special Publication 811 (Guide for the Use of the International System of Units) and the 1959 International Yard and Pound Agreement. All values are exact — none are rounded approximations.

US gallons per minute to liters per minute

The US gallon is defined as exactly 231 cubic inches, which makes it exactly 3.785411784 liters, so one gallon per minute is exactly 3.785411784 liters per minute. The number carries full precision because every step in its derivation is a definition: 231 in³ × (2.54 cm)³ per liter. Plumbing fixtures, swimming pool pumps, and irrigation systems all cross this factor, and because the constant is exact, there is never a reason to round it in a spec.

liters per minute = US gallons per minute × 3.785411784
1 GPM = 3.785411784 L/min — the 231 in³ gallon
The factor is exact by definition.

Worked Examples

Example 1: Convert the US shower-head cap of 2.5 GPM

2.5 × 3.785411784 = 9.46 L/min

Example 2: Convert an 8 GPM domestic supply

8 × 3.785411784 = 30.28 L/min

Example 3: Convert a 50 GPM irrigation pump

50 × 3.785411784 = 189.27 L/min

Common US gallons per minute to liters per minute Conversions

US gallons per minuteliters per minuteContext
1 GPM3.79 L/minThe definitional anchor.
2.5 GPM9.46 L/minThe US legal shower-head cap.
5 GPM18.9 L/minA high-flow shower or small pump.
10 GPM37.9 L/minA pool circulation pump.
100 GPM378.5 L/minA fire truck's pump.

Engineering Context

This is the reciprocal of the L/min to GPM page. The 3.785411784 anchor comes from the gallons to liters volume converter, and the flow rate hub collects all ten flow converters. Pool pumps and fire flows also connect to the pressure family, since pump head and flow are traded against each other on every pump curve.

The trap on this page is which gallon you started with. The factor 3.785411784 belongs to the US liquid gallon; an imperial gallon is 4.54609 L, so an imperial GPM converts to 4.546 L/min, about 20 percent higher. A pump curve or shower specification quoted as "GPM" without a country is ambiguous at exactly this point, and plumbing imported from the United Kingdom or from older Commonwealth documentation is where the discrepancy usually surfaces. If a converted flow looks about a fifth too small, check the gallon before you check the arithmetic.

More: L/min to GPM · GPM to m³/h · gal to L · Flow Rate Guide · Flow Rate Hub

Related Unit Converters

liters per minute to US gallons per minute US gallons per minute to cubic meters per hour Gallons to Liters Flow Rate Conversion Guide Flow Rate Converters

Frequently Asked Questions

How many liters per minute is 1 GPM?

Exactly 3.785411784. The US gallon is 231 in³ = 3.785411784 L by definition, so a gallon per minute is 3.785411784 liters per minute.

Why is the US shower head limited to 2.5 GPM?

The US Energy Policy Act of 1992 capped shower heads at 2.5 GPM at 80 psi to save water and energy. That is 9.46 L/min — the number this converter produces for the legal limit.

How do I convert GPM to L/min quickly?

Multiply by 3.785 for a mental estimate, or by 3.785411784 for exact work. Dividing by 0.2641720524 gives the same answer.