The exact formula
In symbolic form:
The factor applies specifically to US liquid gallons.
Why the factor is exact
One US liquid gallon is defined as exactly 231 cubic inches. One inch is exactly 2.54 centimeters.
Because one liter equals 1,000 cubic centimeters, the gallon can be derived in liters:
1 US gallon = 231 cubic inches
1 cubic inch = 2.54 x 2.54 x 2.54 cubic centimeters
1 cubic inch = 16.387064 cubic centimeters
231 x 16.387064 = 3,785.411784 cubic centimeters
3,785.411784 / 1,000 = 3.785411784 liters
1 US liquid gallon = exactly 3.785411784 litersHow multiplication applies the formula
Each US gallon contributes 3.785411784 liters. Multiplication counts how many of those liter quantities are represented by the input.
Example: 3 US gallons
3 x 3.785411784 = 11.356235352
3 US gallons = 11.356235352 litersExample: 30 US gallons
30 x 3.785411784 = 113.56235352
30 US gallons = 113.56235352 litersAlternative reciprocal formula
One liter equals approximately 0.2641720524 US gallon. Gallons can therefore be divided by that reciprocal value to obtain liters.
Multiplication by the exact factor is clearer and avoids relying on a rounded reciprocal.
Formula example: 12 US gallons
L = 12 x 3.785411784
L = 45.424941408
12 US gallons = 45.424941408 litersRounded to two decimal places, the result is 45.42 liters.
Formula example: 18.5 US gallons
L = 18.5 x 3.785411784
L = 70.030118004
18.5 US gallons = 70.030118004 litersRounded to two decimal places, this is 70.03 liters.
Formula example with a fraction
Convert 2 1/4 US gallons
1 / 4 = 0.25
2 + 0.25 = 2.25 gallons
2.25 x 3.785411784 = 8.517176514
2 1/4 US gallons = 8.517176514 litersExact factor versus shortened factors
| Factor | Typical use | Precision |
|---|---|---|
| 3.785411784 | Exact conversion | Exact factor |
| 3.7854 | Convenient detailed calculation | Close approximation |
| 3.79 | General calculation | Rounded approximation |
| 4 | Mental estimate | Rough approximation |
How much difference does using 4 make?
Consider a quantity of 50 US gallons:
Exact: 50 x 3.785411784 = 189.2705892 L
Estimate: 50 x 4 = 200 L
Difference: 10.7294108 L
Multiplication by 4 is useful for a quick estimate, but the difference grows as the gallon quantity increases.
US gallon compared with other gallon units
| Unit | Liter equivalent |
|---|---|
| US liquid gallon | 3.785411784 L |
| Imperial gallon | 4.54609 L |
| US dry gallon | Approximately 4.404884 L |
The formula on this page applies only to the US liquid gallon.
Reverse formula for liters to US gallons
Divide liters by 3.785411784:
Example: convert 20 liters
20 / 3.785411784 = 5.283441047...
20 liters is approximately 5.28344 US gallonsUse the Liters to US Gallons Converter for the reverse calculation.
Rounding converted values
The conversion factor is exact, but a practical result may still be rounded.
- One decimal place may suit broad tank comparisons.
- Two decimal places are common for general volume conversions.
- Fuel, engineering, or commercial work may require more digits.
- The source measurement may itself be approximate.
Example: round 56.78117676 liters
One decimal place: 56.8 L
Two decimal places: 56.78 L
Three decimal places: 56.781 L
Common formula mistakes
Using 4.54609
That is the Imperial-gallon factor, not the US liquid-gallon factor.
Using a cubic-inch value as liters
One gallon is 231 cubic inches, but cubic inches must be converted before being expressed in liters.
Dividing by 3.785411784
Division by the factor converts liters to US gallons. Gallons to liters requires multiplication.
Assuming every gallon label means US liquid gallons
Confirm the measurement system from the product, country, or specification.
Rounding too early
Keep the complete factor during calculation and round the final result.
The US Gallons to Liters Converter applies the exact factor automatically.
Related US gallons to liters guides
Frequently asked questions
What is the exact US-gallons-to-liters formula?
Liters equal US liquid gallons multiplied by exactly 3.785411784.
Why does one US gallon equal 3.785411784 liters?
A US liquid gallon is exactly 231 cubic inches, and one inch is exactly 2.54 centimeters. Converting the resulting cubic centimeters to liters gives exactly 3.785411784 liters.
Can I use 3.79 as the conversion factor?
Yes, for a rounded result. Use 3.785411784 when greater precision is required.
What is the reverse liters-to-US-gallons formula?
Divide liters by 3.785411784.