There are different types of gallons , so the number of liters depends on which gallon you mean:

• US liquid gallon: approximately 3.785 liters
• US dry gallon: approximately 4.405 liters (less commonly used)
• UK (Imperial) gallon: approximately 4.546 liters

Summary:

Gallon Type| Liters (approx.)
---|---
US liquid gallon| 3.785 L
US dry gallon| 4.405 L
UK (Imperial) gallon| 4.546 L

If you are in the US and mean the standard liquid gallon, use 3.785 liters. If you are in the UK or dealing with Imperial measurements, use 4.546 liters.