A US liquid gallon is exactly 3.785411784 liters.
Gallons to Imperial gallons Converter — gal to imp gal
Convert Gallon (gal) to Imperial gallon (imp gal) using the exact conversion factor (1 gallon = 0.8326741846 imperial gallon). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Gallons to Imperial gallons converter
Converter
Volume Converter
Convert metric, US customary, imperial, cooking, dry, and industrial volume units.
Context values
Some unit families need one extra value for a physically accurate result.
An imperial gallon is exactly 4.54609 liters.
Result = input x 0.003785411784 / 0.00454609.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Gallons to Imperial gallons
Gallon and Imperial gallon appear side by side at fuel pumps and on beverage labels, since the US measures liquids in gallons while most of the world uses liters. Gallon is typically associated with united States (fuel, beverage, and liquid measurement), while Imperial gallon is typically associated with united Kingdom, Canada (some contexts), and other Commonwealth countries.
Formula
imperial gallons = gallons × 0.832674184629
This factor comes from each unit's defined relationship to the category's base unit: 1 gallon equals 0.003785411784 base units, and 1 imperial gallon equals 0.00454609 base units, so dividing one by the other gives the direct gallon-to-imperial gallon factor of 0.832674184629.
Simple example
1 gal × 0.8326741846 = 0.8326741846 imp gal
1 gallon = 0.8326741846 imperial gallons.
Real-world example
10 gal × 0.8326741846 = 8.326741846 imp gal
10 gallons = 8.326741846 imperial gallons.
Conversion table
| Gallon (gal) | Imperial gallon (imp gal) |
|---|---|
| 1 gal | 0.8326741846 imp gal |
| 5 gal | 4.163370923 imp gal |
| 10 gal | 8.326741846 imp gal |
| 25 gal | 20.81685462 imp gal |
| 50 gal | 41.63370923 imp gal |
| 100 gal | 83.26741846 imp gal |
Reverse conversion: Imperial gallon to Gallon
0.8326741846 imp gal × 1.200949926 = 1 gal
0.8326741846 imperial gallons = 1 gallons.
gallons = imperial gallons × 1.2009499255
For a page dedicated to this direction, see Imperial gallon to Gallon.
Gallon vs. Imperial gallon
| Aspect | Gallon | Imperial gallon |
|---|---|---|
| Family | US customary unit | UK/imperial customary unit |
| Typical use | Fuel pump and vehicle fuel-economy measurement in the US | UK fuel and beverage measurement (historically; UK now primarily uses liters for retail) |
| Where it's used | United States (fuel, beverage, and liquid measurement) | United Kingdom, Canada (some contexts), and other Commonwealth countries |
Understanding the Gallon
Gallon (gal) measures volume. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. It is classified as a US customary unit.
Where it's used: United States (fuel, beverage, and liquid measurement)
US gallon vs. imperial gallon. The US liquid gallon (3.785411784 L) and the British imperial gallon (4.54609 L) are different units with the same name; always confirm which one a source is using.
Uses of the Gallon today
- Fuel pump and vehicle fuel-economy measurement in the US
- Beverage and liquid product packaging in the US
- Cooking and recipe measurement in US customary units
History of the Gallon
The US gallon descends from the English wine gallon of 231 cubic inches, a standard used for measuring wine in medieval and early modern England, which the American colonies inherited and retained even after England moved to a different imperial gallon in 1824.
England's 1824 Weights and Measures Act replaced the old wine gallon with a new imperial gallon (based on 10 pounds of water), but the US kept the older 231-cubic-inch definition — which is why the US gallon (3.785 L) and the imperial gallon (4.546 L) differ by about 20% today.
Historical origin. Gallon was not the invention of a single named person; it developed through the process described above.
Understanding the Imperial gallon
Imperial gallon (imp gal) measures volume. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. It is classified as a UK/imperial customary unit.
Where it's used: United Kingdom, Canada (some contexts), and other Commonwealth countries
Imperial gallon vs. US gallon. Britain's 1824 Weights and Measures Act defined a new gallon based on 10 pounds of water, replacing the old wine gallon the US had already adopted — leaving the US (3.785 L) and imperial (4.546 L) gallons about 20% apart today.
Uses of the Imperial gallon today
- UK fuel and beverage measurement (historically; UK now primarily uses liters for retail)
- Commonwealth country liquid measurement in some contexts
History of the Imperial gallon
The imperial gallon was created by Britain's Weights and Measures Act of 1824, defined as the volume of 10 pounds of water, replacing several inconsistent older English gallon definitions (wine gallon, ale gallon, corn gallon) with one standard.
Historical origin. Imperial gallon was not the invention of a single named person; it developed through the process described above.
Gallon — sources
- NIST Handbook 44, Appendix C — General tables of units of measurement, including the US gallon definition.
Imperial gallon — sources
- UK Weights and Measures Act 1824 — Establishes the imperial gallon definition.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many imperial gallons are in 1 gallon?
1 gallon equals 0.8326741846 imperial gallons, using the exact defined conversion factor rather than an estimate.
How do I convert gallon to imperial gallon?
Multiply the gallon value by 0.8326741846. The converter above does this instantly to whatever precision you set.
How do I convert imperial gallon back to gallon?
Use the reverse factor: 1 imperial gallon equals 1.200949926 gallons. You can also use the swap control in the converter above to flip the direction instantly.
What is a gallon?
Gallon (gal) measures volume. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. It is classified as a US customary unit.
What is a imperial gallon?
Imperial gallon (imp gal) measures volume. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. It is classified as a UK/imperial customary unit.
Is the gallon to imperial gallon conversion exact?
Yes. The imperial gallon is defined as exactly 4.54609 liters, about 20% larger than the US gallon. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between us gallon vs. imperial gallon?
The US liquid gallon (3.785411784 L) and the British imperial gallon (4.54609 L) are different units with the same name; always confirm which one a source is using.
Where is the gallon still used today?
United States (fuel, beverage, and liquid measurement)