Gallons vs Liters: Volume Units Compared
Key Difference
1 US gallon = 3.785 liters. 1 imperial gallon = 4.546 liters. There are two different gallons in use: the smaller US gallon and the larger imperial (UK) gallon. Liters are the global standard for volume measurement.
Side-by-Side Comparison
| Property | US Gallon | Imperial Gallon | Liter |
|---|---|---|---|
| Symbol | gal (US) | gal (imp) | L |
| System | US Customary | British Imperial | Metric (SI-accepted) |
| In liters | 3.78541 L | 4.54609 L | 1 L |
| In mL | 3,785.41 mL | 4,546.09 mL | 1,000 mL |
| Used in | USA, some Caribbean | UK (some), Canada (some) | Most countries worldwide |
| Common uses | Fuel, milk, water | Beer (pints), some recipes | Fuel, beverages, science |
Where Each Is Used
The US gallon is used throughout the United States for gasoline, milk, water jugs, and other liquid products. Several Caribbean nations (Belize, Antigua and Barbuda) and some Central American countries also use US gallons. US fuel economy is measured in miles per gallon (MPG) using US gallons.
The imperial gallon was historically used in the UK, Canada, and other Commonwealth countries. However, the UK switched to liters for fuel sales in the 1980s, and Canada completed its switch in the 1970s. Imperial pints (568 mL) are still legally required for draft beer in UK pubs, and some older recipes reference imperial measurements.
Liters are the standard in continental Europe, Asia, Africa, South America, and Oceania. Fuel is sold in liters, beverages are sold in liters and milliliters, and scientific measurements use liters. Fuel economy in metric countries is expressed as liters per 100 kilometers (L/100km), the inverse of MPG.
Conversion Formulas
US Gallons to Liters
L = US gal × 3.78541
Example: 5 gal = 5 × 3.78541 = 18.93 L
Liters to US Gallons
US gal = L × 0.264172
Example: 20 L = 20 × 0.264172 = 5.28 gal
Quick Reference Table
| US Gallons | Liters | Context |
|---|---|---|
| 0.26 | 1 | Standard water bottle |
| 0.5 | 1.89 | Half gallon milk |
| 1 | 3.79 | Gallon milk jug |
| 5 | 18.93 | Jerry can / carboy |
| 10 | 37.85 | Small fish tank |
| 15 | 56.78 | Average car fuel tank |
| 42 | 158.99 | Barrel of oil |
When to Use Which
Use US gallons when buying fuel or milk in the United States, calculating MPG for American vehicles, or following American recipes that reference gallons. Be aware that British recipes using “gallons” mean imperial gallons, which are 20% larger.
Use liters for international communication, travel in metric countries, scientific work, and when buying fuel outside the US. European rental cars display fuel economy in L/100km. A lower L/100km number means better fuel economy.
Quick mental shortcut: multiply US gallons by 4 and subtract 5% to estimate liters. For example, 5 gallons × 4 = 20, minus 1 = 19 liters (actual: 18.93). Close enough for practical estimates.
A Brief History
The gallon has a tangled history. Multiple gallons existed in England for different commodities: the wine gallon (231 cubic inches), the ale gallon (282 cubic inches), and the corn gallon (268.8 cubic inches). The US adopted the wine gallon in 1776. In 1824, Britain standardized on a new imperial gallon defined as the volume of 10 pounds of water (277.42 cubic inches), replacing all older gallons. This is why the US and imperial gallons differ.
The liter was introduced in France in 1795 as part of the metric system, originally defined as the volume of one cubic decimeter (1,000 cubic centimeters). One liter of water at 4°C weighs almost exactly one kilogram, by design. This elegant relationship between volume and mass is one of the metric system's greatest advantages.