How to Convert Gallons to Liters (and Back)
Whether you are filling up a car in a country that sells fuel by the liter, scaling a large recipe, or comparing container sizes, knowing how to convert between gallons and liters is one of the most practical everyday conversions. This guide covers the formula, the US vs UK gallon difference, and common reference values.
What Is a Gallon?
A gallon is a unit of volume used primarily in the United States and, to a lesser extent, the United Kingdom. The two countries use different definitions of the gallon — a fact that causes frequent confusion.
The US liquid gallon equals exactly 3.785411784 liters. It is used for fuel, milk, paint, and other liquids in the United States.
The UK imperial gallon equals exactly 4.54609 liters — about 20% larger than the US gallon. It appears on older British measurements and is still used in some Commonwealth countries.
What Is a Liter?
A liter (L) is the standard metric unit of volume, equal to exactly 1,000 milliliters or 1 cubic decimeter. It is used worldwide for liquids in everyday contexts — fuel, beverages, cooking, and more.
Most countries sell gasoline and diesel by the liter. A standard water bottle is 500 ml (0.5 L). A large soda bottle is typically 2 liters.
The Conversion Formula
US gallons to liters: multiply by 3.78541. For example, 5 gal × 3.78541 = 18.927 L.
Liters to US gallons: multiply by 0.264172. For example, 20 L × 0.264172 = 5.283 gal.
UK gallons to liters: multiply by 4.54609. For example, 5 UK gal × 4.54609 = 22.730 L.
A useful mental shortcut for US gallons: multiply by 3.8 for a quick estimate. It is 0.4% low but good enough for everyday use.
Common Gallon to Liter Conversions
Quick reference for the most frequently needed values (US gallons):
- 1 gallon = 3.785 liters
- 2 gallons = 7.571 liters
- 5 gallons = 18.927 liters
- 10 gallons = 37.854 liters
- 1 liter = 0.264 gallons
- 10 liters = 2.642 gallons
- 20 liters = 5.283 gallons
Real-World Examples
Fuel: A US car with a 15-gallon tank holds about 56.8 liters. If European fuel costs €1.60/L, that fill-up would cost about €91.
Beverages: A US gallon of milk is 3.785 L. A 2-liter soda bottle is about 0.53 US gallons.
Recipes: A US recipe calling for 1 gallon of liquid requires 3.785 L — roughly four standard metric bottles.
Swimming pools: A small backyard pool holding 5,000 gallons contains about 18,927 liters.
Fuel Economy: Gallons, Liters, and International Comparisons
When comparing car fuel efficiency between the US and Europe, you need to convert both distance and volume units. A European car rated at 6 L/100km has a fuel economy of 235.215 ÷ 6 = 39.2 US MPG. A US car rated at 30 MPG uses 235.215 ÷ 30 = 7.84 L/100km. Converting to a common unit lets you compare models across markets.
Fuel prices also require conversion for international comparison. If European petrol costs €1.60 per liter, that is €1.60 × 3.785 = €6.05 per US gallon equivalent — making European fuel approximately 70% more expensive than US prices at typical rates. This partly explains why European cars tend to have smaller engines and higher fuel efficiency than American ones.
Large-scale fuel purchases involve thousands of gallons or tens of thousands of liters. A commercial aircraft like a Boeing 737 holds about 26,000 liters (6,870 US gallons) of fuel. An oil tanker carries millions of gallons. In these contexts, a small unit conversion error compounds into enormous financial and logistical consequences.
The History of the Gallon
The word "gallon" derives from the Old North French "galon," related to a liquid measure used in medieval England. Before standardization, many different gallons existed: the wine gallon, the ale gallon, and the Winchester gallon each held different volumes, causing persistent confusion in trade.
The US gallon was standardized in 1707 based on the Queen Anne wine gallon of 231 cubic inches (3.785 L). The UK imperial gallon was standardized in 1824 at 277.42 cubic inches (4.546 L) — about 20% larger. Canada used the imperial gallon until 1979, when it switched to liters.
Today, the gallon is used primarily in the US for fuel, beverages, and paint. A few Caribbean nations and some agricultural contexts in the UK retain gallon measurements. For international commerce, liters are the universal standard — understanding the US/UK gallon difference is important when reading older documents or purchasing goods from either country.
Conclusion
1 US gallon = 3.78541 liters. 1 UK imperial gallon = 4.54609 liters. Always confirm which gallon standard is being used before converting — the 20% difference matters for fuel economy comparisons and large-scale recipes. Use our free volume converter for instant results.