How to Convert Gallons to Liters: Formula, US vs Imperial & Practical Uses
Learn how to convert gallons to liters with the precise formula, the difference between US and Imperial gallons, and use cases for cooking and fuel.
February 21, 2026
Volume conversions between gallons and liters come up frequently in everyday life, from filling up your car's gas tank abroad to following international recipes. Understanding the relationship between these units, and the critical difference between US and Imperial gallons, helps you avoid costly mistakes.
The Gallon to Liter Formula
The most commonly used gallon is the US gallon. One US gallon equals 3.78541 liters. To convert any volume from US gallons to liters, multiply by 3.78541.
Formula: liters = US gallons x 3.78541
For a quick approximation, multiply by 3.8. For example, 5 US gallons x 3.785 = 18.93 liters.
US Gallon vs. Imperial Gallon
This is a critical distinction that catches many people off guard. The US gallon and the Imperial (British) gallon are not the same size:
- 1 US gallon = 3.78541 liters
- 1 Imperial gallon = 4.54609 liters
The Imperial gallon is about 20% larger than the US gallon. This difference matters enormously in contexts like fuel economy, where a car getting 30 miles per Imperial gallon is actually more efficient than one getting 30 miles per US gallon.
Quick Reference Conversion Table
- 1 US gallon = 3.785 liters
- 2 US gallons = 7.571 liters
- 5 US gallons = 18.927 liters
- 10 US gallons = 37.854 liters
- 15 US gallons = 56.781 liters
- 20 US gallons = 75.708 liters
- 50 US gallons = 189.271 liters
- 100 US gallons = 378.541 liters
Practical Use Cases
Fuel and Gas Stations
When driving in Europe, you will find fuel sold by the liter. If you are used to thinking in gallons, knowing the conversion helps you estimate costs. A 15-gallon (US) fuel tank holds about 56.8 liters. Gas prices per liter in Europe might seem low compared to per-gallon prices in the US, but multiply by 3.785 to get the true per-gallon equivalent.
Cooking and Beverages
Many American recipes use gallon measurements for large quantities of liquids, such as soups, beverages, or brines. When adapting these recipes for metric kitchens, one gallon of water or milk equals approximately 3.8 liters. For smaller quantities, remember that a US quart (1/4 gallon) is about 0.946 liters.
Swimming Pools and Water Features
Pool capacity is often stated in gallons in the United States. A typical residential swimming pool holds around 15,000 to 30,000 US gallons, which translates to approximately 56,781 to 113,562 liters. This conversion is essential for calculating chemical treatments and water costs.
Reverse Conversion: Liters to Gallons
To convert liters back to US gallons, divide by 3.78541 or multiply by 0.264172. For example, 20 liters x 0.264172 = 5.28 US gallons.
Tips for Quick Estimation
A simple rule of thumb: 1 gallon is roughly 4 liters. While not perfectly precise (the actual value is 3.785), this approximation works well for quick mental math. Conversely, 1 liter is roughly a quarter of a gallon. These shortcuts help you navigate between measurement systems without needing a calculator for everyday situations.