Gallons to Liters: US vs UK Gallons, Fluid Ounces, and Every Liquid Conversion You Need
A gallon is a gallon, right? Not quite. The US gallon and the UK (Imperial) gallon are different sizes, and confusing them leads to real problems when comparing fuel economy, following recipes, or buying products internationally. This guide covers everything about liquid volume conversions, including the differences that trip people up most.
US Gallon vs UK (Imperial) Gallon
This is the most important thing to understand about gallons: the US and UK versions are not the same.
- 1 US gallon = 3.785 liters
- 1 UK (Imperial) gallon = 4.546 liters
The Imperial gallon is about 20% larger than the US gallon. This difference has practical consequences. When a car is rated at 30 mpg in the UK, it means 30 Imperial miles per Imperial gallon, which is equivalent to about 25 mpg in US terms. A recipe calling for "1 gallon of water" means 3.785 liters if the recipe is American, but 4.546 liters if it is British.
The historical reason: the US gallon was based on the English wine gallon (231 cubic inches), while the Imperial gallon was defined in 1824 as the volume of 10 pounds of water at a specific temperature (277.42 cubic inches).
Gallons to Liters Conversion Table
| US Gallons | Liters | UK Gallons | Liters |
|---|---|---|---|
| 0.5 | 1.89 | 0.5 | 2.27 |
| 1 | 3.79 | 1 | 4.55 |
| 2 | 7.57 | 2 | 9.09 |
| 3 | 11.36 | 3 | 13.64 |
| 5 | 18.93 | 5 | 22.73 |
| 10 | 37.85 | 10 | 45.46 |
| 15 | 56.78 | 15 | 68.19 |
| 20 | 75.71 | 20 | 90.92 |
| 50 | 189.27 | 50 | 227.30 |
Fluid Ounces: Another US vs UK Problem
Just like gallons, fluid ounces differ between the US and UK systems:
- 1 US fluid ounce = 29.57 ml
- 1 UK fluid ounce = 28.41 ml
The difference is small (about 4%), but it compounds over larger quantities. Confusingly, there are 128 US fluid ounces in a US gallon, but 160 UK fluid ounces in an Imperial gallon. So while the individual UK fluid ounce is slightly smaller, there are more of them in an Imperial gallon, making the Imperial gallon larger overall.
Common Liquid Volumes in Everyday Life
Here are familiar container sizes to help you estimate volumes:
- Shot glass: 44 ml (1.5 US fl oz)
- Standard soda can: 355 ml (12 US fl oz)
- Water bottle: 500 ml (16.9 US fl oz)
- Wine bottle: 750 ml (25.4 US fl oz)
- Quart of milk (US): 946 ml (32 US fl oz)
- Large soda bottle: 2 liters (67.6 US fl oz)
- Gallon of milk (US): 3,785 ml (128 US fl oz)
The Confusing Pint
The pint is one of the most confusing volume units because it differs significantly between the US and UK:
- 1 US pint = 473 ml (16 US fl oz)
- 1 UK pint = 568 ml (20 UK fl oz)
A UK pint is about 20% larger than a US pint. This is why a "pint of beer" in a British pub (568 ml) is noticeably more generous than a US pint (473 ml). If you order a pint in Ireland, the UK, or Australia, you get the Imperial pint. In the US, you get the smaller US pint.
Converting Fuel Prices: Price Per Liter to Price Per Gallon
When traveling internationally, you often need to compare fuel prices. Most countries price fuel per liter, while the US prices per gallon.
To convert price per liter to price per US gallon, multiply by 3.785. For example:
- Fuel at $1.50 per liter = $5.68 per US gallon
- Fuel at 1.80 euros per liter = 6.81 euros per US gallon
To convert price per US gallon to price per liter, divide by 3.785. For example:
- Fuel at $3.50 per gallon = $0.92 per liter
Remember to also account for currency exchange rates when comparing fuel costs between countries.
Quarts and Cups: The Full US Liquid Volume Hierarchy
The US liquid volume system follows this structure:
| Unit | Equivalent | Milliliters |
|---|---|---|
| 1 teaspoon | 1/6 fl oz | 5 ml |
| 1 tablespoon | 1/2 fl oz | 15 ml |
| 1 cup | 8 fl oz | 240 ml |
| 1 pint | 2 cups | 473 ml |
| 1 quart | 2 pints / 4 cups | 946 ml |
| 1 gallon | 4 quarts / 8 pints | 3,785 ml |
Use our Liquid Volume Converter for instant, accurate conversions between any liquid volume units.
Frequently Asked Questions
How many liters in a gallon?
A US gallon contains 3.785 liters. A UK (Imperial) gallon contains 4.546 liters. When someone says "gallon" without specifying, in the US it means the US gallon (3.785 L). In the UK, Canada, and other Commonwealth countries, it historically meant the Imperial gallon, though most have now switched to liters.
Why are US and UK gallons different sizes?
The US gallon (3.785 L) was based on the English wine gallon of 231 cubic inches, which the American colonies adopted before independence. The UK redefined its gallon in 1824 as the Imperial gallon (4.546 L), based on the volume of 10 pounds of water. The US kept the older, smaller definition.
How do I convert fuel economy between mpg and L/100km?
To convert US mpg to L/100km, divide 235.21 by the mpg value. For example, 30 US mpg = 235.21 / 30 = 7.84 L/100km. To convert UK mpg to L/100km, divide 282.48 by the mpg value. Note that UK mpg and US mpg are different because the gallons are different sizes.
Is a UK pint bigger than a US pint?
Yes. A UK pint is 568 ml (20 UK fl oz), while a US pint is 473 ml (16 US fl oz). The UK pint is about 20% larger. This is why beer servings in British pubs are larger than American pints.
How many fluid ounces are in a liter?
There are 33.81 US fluid ounces in a liter, or 35.20 UK fluid ounces in a liter. A liter is slightly more than a US quart (32 fl oz) but less than a UK quart (40 UK fl oz).