Gallons to Liters — Volume Conversion

Gallons to liters means converting a volume from one unit to another. In most US problems, $1$ gallon means $1$ US liquid gallon, so you multiply by $3.785411784$:

$$\text{liters} = \text{gallons} \times 3.785411784$$

If the context is imperial instead, use $4.54609$ liters per gallon. The condition matters because a US gallon and an imperial gallon are different units.

For a quick check, a US gallon is a little less than $4$ liters.

Gallons To Liters Formula

$$1\ \text{US liquid gallon} = 3.785411784\ \text{liters}$$ $$1\ \text{imperial gallon} = 4.54609\ \text{liters}$$

A gallon and a liter are both units of volume. The amount of liquid stays the same. Only the unit name changes.

That is why the number changes while the physical quantity does not. Since a gallon is larger than a liter, the number of liters is bigger than the number of gallons.

Example: $5$ Gallons To Liters

Assume the problem means US liquid gallons.

Use the conversion formula:

$$\text{liters} = 5 \times 3.785411784$$

Now multiply:

$$5 \times 3.785411784 = 18.92705892$$

So

$$5\ \text{gallons} \approx 18.93\ \text{liters}$$

For most everyday uses, $18.93$ liters is a practical final answer. In a technical setting, keep more digits if the given data is more precise.

Common Gallons To Liters Mistakes

Using The Wrong Gallon

This is the main source of wrong answers. In a US context, "gallon" usually means US liquid gallon. In a UK or older imperial context, it may mean imperial gallon.

For $5$ gallons, that difference is large enough to matter:

$$5 \times 3.785411784 = 18.92705892$$ $$5 \times 4.54609 = 22.73045$$

Those answers describe different starting units, so they are not interchangeable.

Rounding Too Early

If you round $3.785411784$ to $3.8$ before multiplying, small errors can build up. Keep the more accurate factor until the end, then round the final answer.

Reversing The Formula

Gallons to liters means multiply by liters per gallon. Liters to gallons goes the other way:

$$\text{gallons} = \frac{\text{liters}}{3.785411784}$$

for US liquid gallons.

When Gallons To Liters Is Used

This conversion appears in fuel quantities, beverage containers, aquarium and tank sizes, recipe scaling, and travel situations where one source uses gallons and another uses liters.

It also appears in unit-conversion word problems. The point is usually to choose the correct factor first, then compute carefully.

Try A Similar Conversion

Try your own version with $2.5$ gallons or $12$ gallons, and decide first whether the context is US liquid or imperial. If you want to check your setup afterward, solve a similar problem and compare both the arithmetic and the unit choice.