What Is Imperial Gallon?
An imperial gallon is a unit used to measure how much space a liquid takes up. It is part of the old British system of measurement and is still used for things like fuel economy and some liquid products in a few countries.
The imperial gallon is bigger than the US gallon. This means one imperial gallon can hold more liquid than one US gallon.
Definition
The imperial gallon is a unit of volume. Volume means how much space something fills.
- 1 imperial gallon equals exactly 4.54609 liters.
- 1 imperial gallon equals 4 imperial quarts.
- 1 imperial gallon equals 8 imperial pints.
- 1 imperial gallon equals 160 imperial fluid ounces.
- 1 imperial gallon is about 1.2 times bigger than a US liquid gallon.
When people say “gallon” in the United Kingdom and some other countries, they usually mean the imperial gallon, unless they clearly say it is a US gallon.
History / Origin
The imperial gallon started in the United Kingdom in the early 1800s. Before that time, there were many different gallons in use, which caused confusion in trade and daily life.
In 1824, the British government passed a law called the Weights and Measures Act. This law created a new standard system called the Imperial system. The imperial gallon became the official gallon in this system.
The original idea was based on water. One imperial gallon was set as the volume of 10 pounds of pure water at a certain temperature and air pressure. Later, this was changed to an exact metric value, 4.54609 liters, so it would be clear and easy to compare with the metric system.
Over time, many countries moved from the imperial system to the metric system, but the imperial gallon is still known and sometimes used, especially in places that used to be part of the British Empire.
Symbol & Abbreviation
The imperial gallon has several common short forms.
- imp gal is the clearest short form for imperial gallon.
- gal is sometimes used, but this can be confusing because the US gallon also uses gal.
- gallon written in full is often used in everyday language.
To avoid mistakes, it is best to write “imp gal” when you mean the imperial gallon, especially in technical writing, on labels or in conversion tables.
Current Use Around the World
The imperial gallon is no longer the main legal unit in most places, but it is still used in some ways.
- United Kingdom Fuel is sold in liters, but fuel economy for cars is often given in miles per imperial gallon. Some people also talk about swimming pool size and some liquids in imperial gallons.
- Canada Uses the metric system officially, but many drivers still talk about fuel use in miles per imperial gallon, and older books and manuals may use imperial gallons.
- Caribbean and some Commonwealth countries A few countries still use the imperial gallon for fuel or other liquids, although many are slowly changing to liters.
- International trade and science Mostly use liters and cubic meters instead of gallons, but the imperial gallon still appears in older standards, manuals and historical data.
Because there are both imperial gallons and US gallons, many modern businesses and laws prefer liters to avoid confusion.
Example Conversions
Here are some easy to read examples that show how imperial gallons relate to other units.
Imperial gallons to liters
- 1 imperial gallon = 4.54609 liters
- 2 imperial gallons = 9.09218 liters
- 5 imperial gallons = 22.73045 liters
- 10 imperial gallons = 45.4609 liters
Liters to imperial gallons
To change liters to imperial gallons, divide the liters by 4.54609.
- 5 liters ≈ 1.10 imperial gallons
- 10 liters ≈ 2.20 imperial gallons
- 20 liters ≈ 4.40 imperial gallons
- 50 liters ≈ 11.00 imperial gallons
Imperial gallons to US gallons
One imperial gallon is larger than one US gallon.
- 1 imperial gallon ≈ 1.20095 US liquid gallons
- 5 imperial gallons ≈ 6.00 US liquid gallons
- 10 imperial gallons ≈ 12.01 US liquid gallons
Imperial gallons to other imperial units
- 1 imperial gallon = 4 imperial quarts
- 1 imperial gallon = 8 imperial pints
- 1 imperial gallon = 160 imperial fluid ounces
- 0.5 imperial gallon = 2 quarts = 4 pints
Related Units
The imperial gallon is part of a family of volume units. Knowing the related units makes it easier to convert and compare.
- Imperial fluid ounce Smallest common imperial liquid unit. 160 in 1 imperial gallon.
- Imperial gill Old unit. 5 fluid ounces in 1 gill, 32 gills in 1 imperial gallon.
- Imperial pint 8 fluid ounces. 8 pints in 1 imperial gallon.
- Imperial quart 2 pints. 4 quarts in 1 imperial gallon.
- US liquid gallon The US version of the gallon. Smaller than the imperial gallon.
- US quart, pint, fluid ounce US volume units that match the US gallon, not the imperial gallon.
- Liter Main metric volume unit for liquids. 1 imperial gallon is 4.54609 liters.
- Cubic meter Metric unit for larger volumes. 1 cubic meter equals 1000 liters, which is about 220 imperial gallons.
FAQs
Is an imperial gallon the same as a US gallon?
No, they are not the same. An imperial gallon is bigger. One imperial gallon is about 1.2 US gallons. If you mix them up, your numbers will be wrong, so always check which gallon is meant.
How many liters are in an imperial gallon?
There are exactly 4.54609 liters in 1 imperial gallon. A quick way to remember is that it is a little more than 4 and a half liters.
Where is the imperial gallon still used today?
It is mainly used in the United Kingdom, Canada and some other countries for things like car fuel economy in miles per imperial gallon and in some older rules, books and tools. Most shops, however, use liters now.
Why is the imperial gallon larger than the US gallon?
The two gallons were created from different historical rules and reference volumes. The British standard settled on a definition based on 10 pounds of water, which made the imperial gallon larger than the US gallon that kept an older wine gallon size.
How can I quickly change imperial gallons to liters in my head?
For a simple estimate, you can multiply by 4.5. For example, 2 imperial gallons is about 9 liters, 5 imperial gallons is about 22.5 liters. For exact work, use 4.54609.
Why do some cars show miles per gallon if fuel is sold in liters?
In countries like the UK and Canada, people used to buy fuel in imperial gallons. Even after fuel pumps changed to liters, many drivers and car makers kept using miles per imperial gallon to talk about fuel use, because they were already used to it.
Can I use imperial gallons in science or engineering?
In modern science and engineering, the metric system is preferred, especially liters and cubic meters. You may still see imperial gallons in older books, building plans or fuel data, but new work usually uses metric units.
How do I know if a recipe uses imperial or US gallons?
Look at where the recipe comes from. If it is from the UK or another country that used the imperial system, it may mean imperial gallons. If it is from the United States, it almost always means US gallons. When in doubt, check the book, website notes, or convert to liters and work in metric.