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

• 1 US liquid gallon = approximately 3.785 liters
• 1 UK (Imperial) gallon = approximately 4.546 liters
• 1 US dry gallon = approximately 4.404 liters

The most commonly referenced is the US liquid gallon, which equals about 3.785 liters.