How To Convert Gallons To Liters Calculator
One decision comes before the arithmetic — which gallon you have — and once that is settled the whole conversion is a single multiplication by an exact factor.
Volume in liters
56.7812
- Same volume in milliliters
- 56,781.1768
- Same count read as US gallons
- 56.7812
- Same count read as Imperial gallons
- 68.1914
- Gap between the two definitions
- 11.4102
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
L = gal x 3.785411784
- gal
- Volume in gallons — a count, not yet a metric quantity
- 3.785411784
- Liters in one US liquid gallon, defined as 231 cubic inches
- 4.54609
- Liters in one Imperial gallon, historically ten pounds of water
- L
- Volume in liters; multiply by 1000 for milliliters
How to check the result by hand
- 1
Establish which gallon your source means
Before multiplying anything, decide whether the figure is a US liquid gallon of 3.785411784 liters or an Imperial gallon of 4.54609 liters. The two differ by a factor of 1.2009499255, which is roughly 20.095 percent, and no later step can recover from choosing wrong here. Country of origin, the units printed alongside it, or an explicit label are the fastest clues.
- 2
Multiply by the exact factor
Fifteen US gallons times 3.785411784 gives 56.78117676 liters. Use the full factor rather than a shortened one and keep every digit the calculator returns; the multiplication is the only operation involved, so there is nothing to gain by rounding part way through.
- 3
Shift to milliliters when liters are awkwardly small
Multiply by a thousand: 56.78117676 liters is 56781.17676 milliliters. Because metric prefixes are decimal, this is a shift of the point rather than a fresh conversion, and it is the cheapest way to present a result without a long decimal string.
- 4
Cross-check against the other standard
The same count of 15 read as Imperial gallons gives 68.19135 liters, which is 11.41017324 liters more than the US reading. An answer that lands between those two figures suggests the standards have been mixed; one that matches either exactly confirms the choice made in the first step held.
- 5
Round once, at the end
A tank of 12 US gallons is 45.424941408 liters, and the exact value is the one to retain if it feeds any further calculation. Round only the number a person will actually read, and match the precision of the original measurement rather than the precision of your calculator.
For worked examples, common mistakes and the limits of this formula, read the full How To Convert Gallons To Liters page.