An imperial gallon is exactly 4.54609 liters.
Imperial gallons to Gallons Converter — imp gal to gal
Convert Imperial gallon (imp gal) to Gallon (gal) using the exact conversion factor (1 imperial gallon = 1.200949926 gallon). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Imperial gallons to 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.
A US liquid gallon is exactly 3.785411784 liters.
Result = input x 0.00454609 / 0.003785411784.
Volume uses the cubic meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Imperial gallons to Gallons
Imperial gallon and 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. Imperial gallon is typically associated with united Kingdom, Canada (some contexts), and other Commonwealth countries, while Gallon is typically associated with united States (fuel, beverage, and liquid measurement).
Formula
gallons = imperial gallons × 1.2009499255
This factor comes from each unit's defined relationship to the category's base unit: 1 imperial gallon equals 0.00454609 base units, and 1 gallon equals 0.003785411784 base units, so dividing one by the other gives the direct imperial gallon-to-gallon factor of 1.2009499255.
Simple example
1 imp gal × 1.200949926 = 1.200949926 gal
1 imperial gallon = 1.200949926 gallons.
Real-world example
10 imp gal × 1.200949926 = 12.00949926 gal
10 imperial gallons = 12.00949926 gallons.
Conversion table
| Imperial gallon (imp gal) | Gallon (gal) |
|---|---|
| 1 imp gal | 1.200949926 gal |
| 5 imp gal | 6.004749628 gal |
| 10 imp gal | 12.00949926 gal |
| 25 imp gal | 30.02374814 gal |
| 50 imp gal | 60.04749628 gal |
| 100 imp gal | 120.0949926 gal |
Reverse conversion: Gallon to Imperial gallon
1.200949926 gal × 0.8326741846 = 1 imp gal
1.200949926 gallons = 1 imperial gallons.
imperial gallons = gallons × 0.832674184629
For a page dedicated to this direction, see Gallon to Imperial gallon.
Imperial gallon vs. Gallon
| Aspect | Imperial gallon | Gallon |
|---|---|---|
| Family | UK/imperial customary unit | US customary unit |
| Typical use | UK fuel and beverage measurement (historically; UK now primarily uses liters for retail) | Fuel pump and vehicle fuel-economy measurement in the US |
| Where it's used | United Kingdom, Canada (some contexts), and other Commonwealth countries | United States (fuel, beverage, and liquid measurement) |
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.
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.
Imperial gallon — sources
- UK Weights and Measures Act 1824 — Establishes the imperial gallon definition.
Gallon — sources
- NIST Handbook 44, Appendix C — General tables of units of measurement, including the US gallon definition.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many gallons are in 1 imperial gallon?
1 imperial gallon equals 1.200949926 gallons, using the exact defined conversion factor rather than an estimate.
How do I convert imperial gallon to gallon?
Multiply the imperial gallon value by 1.200949926. The converter above does this instantly to whatever precision you set.
How do I convert gallon back to imperial gallon?
Use the reverse factor: 1 gallon equals 0.8326741846 imperial gallons. You can also use the swap control in the converter above to flip the direction instantly.
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.
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.
Is the imperial gallon to gallon conversion exact?
Yes. The US liquid gallon is defined as exactly 231 cubic inches, equal to 3.785411784 liters. 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 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.
Where is the imperial gallon still used today?
United Kingdom, Canada (some contexts), and other Commonwealth countries