What is US gallon?
A US gallon is a volume unit equal to 128 US fluid ounces, or approximately 3.785 litres. It is the standard unit for fuel, milk, and other liquid products in the United States.
Real-world uses
US gallons are used for fuel pricing and vehicle fuel economy (miles per gallon) in the United States. Milk, water, and paint are commonly sold in gallon containers. Pool volumes and water heater capacities are specified in gallons.
History
The US gallon is based on the English wine gallon of 231 cubic inches, which was defined by Queen Anne in 1707. When Britain adopted the Imperial gallon in 1824 (based on water weight), the US retained the older wine gallon standard.
Common mistakes
Confusing US gallons with Imperial gallons: a US gallon is about 3.785 litres while an Imperial gallon is about 4.546 litres—roughly 20% larger. This causes major confusion when comparing fuel economy between US and UK figures.
What is Imperial gallon?
An Imperial gallon is a volume unit used in the United Kingdom equal to approximately 4.546 litres. It is larger than the US gallon and is commonly referenced for fuel efficiency (miles per gallon) in the UK.
Real-world uses
Imperial gallons are used in the United Kingdom, Canada (for some purposes), and several Caribbean countries. British fuel economy was historically quoted in miles per Imperial gallon. Older Commonwealth-era recipes and industrial specifications may reference Imperial gallons.
History
The Imperial gallon was established by the British Weights and Measures Act of 1824 as the volume occupied by 10 pounds of water at 62°F (≈ 17°C). It replaced several older gallon definitions including the wine gallon (retained by the US) and the ale gallon.
Common mistakes
Assuming the Imperial gallon equals the US gallon. The Imperial gallon is about 4.546 litres versus 3.785 litres for the US gallon. Converting mpg figures between the two systems without adjusting for gallon size gives misleading results.
When is this conversion used?
Fuel economy, beverage volumes, and liquid measurements frequently require converting between litres and US gallons, especially for automotive and cooking contexts across different markets.
Worked examples
1 US gallon = 0.83267418 Imperial gallon
1 Imperial gallon = 4.54609 litre
How to convert US gallon to Imperial gallon
To convert US gallon to Imperial gallon, multiply the value by 0.83267418.
To convert Imperial gallon back to US gallon, multiply by 1.20094993.
Measurement standards
The cubic metre is the SI derived unit of volume. The litre, equal to exactly one cubic decimetre (0.001 m³), is accepted by the BIPM for use alongside SI units. Both the lowercase "l" and uppercase "L" are approved symbols for the litre.
Did you know?
An Olympic swimming pool holds 2,500 cubic metres of water — about 2.5 million litres. The Amazon River discharges roughly 209,000 cubic metres per second, enough to fill 84 Olympic pools every single second.
Quick reference: US gallon to Imperial gallon
| US gallon | Imperial gallon |
|---|---|
| 0.1 | 0.08326742 |
| 0.5 | 0.41633709 |
| 1 | 0.83267418 |
| 2 | 1.66534837 |
| 5 | 4.16337092 |
| 10 | 8.32674185 |
| 25 | 20.81685462 |
| 50 | 41.63370923 |
| 100 | 83.26741846 |
| 250 | 208.16854616 |
| 500 | 416.33709231 |
| 1,000 | 832.67418463 |
Common values
| US gallon | Imperial gallon | |
|---|---|---|
| A teaspoon | 0.00132086 US gallon | 0.00109985 Imperial gallon |
| A cup of coffee | 0.06604301 US gallon | 0.05499231 Imperial gallon |
| A water bottle | 0.13208603 US gallon | 0.10998462 Imperial gallon |
| A bathtub | 79.25161571 US gallon | 65.99077449 Imperial gallon |
| A swimming pool (Olympic) | 660,430.13089537 US gallon | 549,923.12074772 Imperial gallon |
Available Volume units
More US gallon conversions
- Convert US gallon to litre
- Convert US gallon to millilitre
- Convert US gallon to cubic metre
- Convert US gallon to Imperial gallon
- Convert US gallon to US fluid ounce
- Convert US gallon to Imperial fluid ounce
- Convert US gallon to teaspoon (metric)
- Convert US gallon to tablespoon (metric)
- Convert US gallon to cubic centimetre