The formula
L = US gal × 3.785411784
Where the factor comes from — each unit by its definition, then its size in SI:
1 US gal = 231 × in³ = 0.003785411784 m³1 L = m³ / 1000 = 0.001 m³
Dividing the two SI sizes gives the factor: 3.785411784, exact — every step above is a definition, not a measurement. The reverse factor is 0.264172052358.
The cubic metre is the SI unit of volume; the litre is exactly one thousandth of it. The US and UK gallons are different sizes, which is why a fuel-economy figure in mpg depends on which country printed it.
Worked examples
- A soft-drink bottle: 0.528344 US gal = 2 L — 0.528344 × 3.785411784 = 2
- A paint bucket: 5 US gal = 18.9271 L — 5 × 3.785411784 = 18.9271
- A water tank (1 m³): 264.172 US gal = 1,000 L — 264.172 × 3.785411784 = 1,000
- A drinks can (330 mL): 0.0871768 US gal = 0.33 L — 0.0871768 × 3.785411784 = 0.33
Frequently asked questions
How many litres is 1 US gal?
1 US gal = 3.785411784 L, exactly, from the unit definitions.
How do I convert litres back to US gallons?
Divide by 3.785411784 — or multiply by 0.264172052358: 1 L = 0.264172052358 US gal.