How many Litres are in a British gallon?

A British gallon contains 4.54609 litres. This makes converting between gallons and litres straightforward – simply multiply or divide by 4.54609.

Quick Answer

There are 4.54609 litres in 1 British gallon.

What is a Gallon?

A gallon is a unit of volume measurement used in both the imperial and US customary systems. It has different definitions in the two systems:

  • Imperial gallon – used in the UK and some other countries which were part of the British Empire. Equal to 4.54609 litres.
  • US gallon – used in the US and some Latin American countries. Equal to 3.78541 litres.

The imperial gallon is about 20% larger than the US gallon. This difference can cause confusion when converting between the two units.

Origin of the Gallon

The word gallon comes from the Old French word galon, meaning a liquid measure. In the 13th century, a gallon was defined as the volume occupied by 10 pounds of water under defined conditions. Over time, there were minor variations in the exact volume of a gallon in different parts of Britain.

It was not until 1824 that the imperial gallon was standardised as containing 10 pounds (4.54 kg) of water. The imperial system of units was widely adopted in the British Empire during the 19th century. Hence the imperial gallon became the standard definition in the UK, its colonies, and countries under British influence.

The US customary system derives from earlier English units used in the early colonies. The US gallon is based on the earlier English wine gallon and is about 17% smaller than the imperial gallon.

Uses of the Gallon

The gallon unit is commonly used to measure volumes of liquid in both everyday and commercial contexts. Some examples include:

  • Fuel – petroleum products like gasoline are sold by the gallon in many countries.
  • Milk – often sold by the gallon.
  • Beverages – beer, wine, etc are sometimes sold by the gallon.
  • Engine capacity – expressed in litres, but sometimes referred to in gallons in the UK.
  • Water usage – residential water meters measure consumption in gallons.

The rise of the metric system has led to decreased use of the gallon in many countries. However, it remains popular in day to day usage, especially in the US and Commonwealth countries.

How Many Litres in a Gallon?

Now that we’ve covered some essential background on the gallon, let’s get to the crux of this article – how many litres are there in 1 imperial gallon?

The Answer

There are 4.54609 litres in 1 imperial gallon.

This figure is based on the official definition of the imperial gallon adopted in 1824. By definition, 1 imperial gallon contains 10 pounds (4.54 kg) of water at a temperature of 62°F (16.67°C).

One litre is defined as the volume occupied by 1 kilogram of water. So 4.54 kg of water occupies 4.54 litres. Therefore, by definition, 1 imperial gallon is exactly 4.54609 litres.

Conversion Formula

The conversion between imperial gallons and litres can be summarized as:

  • 1 imperial gallon = 4.54609 litres
  • 1 litre = 0.219969 imperial gallons

Expressed as a formula:

  • Litres = Gallons x 4.54609
  • Gallons = Litres x 0.219969

So to convert between the units:

  • To convert gallons to litres, multiply by 4.54609
  • To convert litres to gallons, multiply by 0.219969

Let’s look at some examples:

  • 5 gallons x 4.54609 = 22.7305 litres
  • 15 litres x 0.219969 = 3.29954 gallons

Patterns in the Conversion

Some observations can be made about the gallons to litres conversion:

  • 1 gallon is very close to 4.5 litres
  • 2 gallons is very close to 9 litres
  • 5 gallons is very close to 22.5 litres (or 45/2 litres)

So while the exact conversion factor is 4.54609, for mental math or rough estimates, it’s handy to remember:

  • 1 gallon ≈ 4.5 litres
  • 2 gallons ≈ 9 litres
  • 5 gallons ≈ 22.5 litres

The inverse is also approximately true – multiply litres by 0.22 to get a rough number of gallons.

Converting Gallons and Litres in Everyday Use

Now that we’ve looked at the gallon-litre conversion in detail, let’s consider some practical examples of how it can be useful in daily life:


Many recipe books, especially older British ones, provide ingredient quantities in imperial units like gallons. When following such recipes, you need to convert the gallons to millilitres or litres to measure out ingredients correctly.

As an example, if a recipe calls for 1⁄4 gallon of milk, convert it to litres as:

1⁄4 gallon x 4.54609 litres/gallon = 1.1365 litres

So you would measure out about 1.14 litres of milk.

Fuel Efficiency

In the UK, fuel efficiency for vehicles is usually expressed as miles per imperial gallon (mpg). To compare against fuel efficiency in litres/100 km used elsewhere, convert miles/gallon to litres/100 km using the gallons to litres conversion.

For example, a mileage of 40 mpg converts to:

100 km / (40 miles/gallon x 4.54609 litres/gallon x 1.60934 km/mile ) = 5.917 litres/100 km

Water Usage

Residential water meters in the UK display volume in imperial gallons. To compare your household usage with typical figures provided in litres, convert the gallons to litres.

If your meter shows 5,000 gallons used in a month, then:

5,000 gallons x 4.54609 litres/gallon = 22,730 litres

So you would quote your monthly usage as 22,730 litres.

Fuel Purchases

When filling up your car’s petrol tank in the UK, the pump displays the volume in litres but your mental math may be easier in gallons. To estimate cost using a price per gallon, quickly convert the price to per litre using the ratio of 4.54609 litres per gallon.

If petrol costs £1.20 per gallon, then:

1 gallon = 4.54609 litres

£1.20 per gallon x (1 gallon / 4.54609 litres) = £0.264 per litre

So petrol costs about £0.26 per litre.


Some beverages like wine or fruit juice are sold by the gallon. To relate the quantity to the more familiar litres, make the conversion.

If you purchase a 3 gallon jug of apple juice, convert it to:

3 gallons x 4.54609 litres/gallon = 13.64 litres

So you would say the container has close to 14 litres of juice.

Gallons to Litres Conversion Table

For easy reference, here is a conversion table showing some common quantities in gallons and their equivalent in litres:

Gallons Litres
1 4.55
2 9.09
3 13.64
5 22.73
10 45.46
15 68.19
20 90.92
25 113.65
30 136.38
40 181.84
50 227.30

Other Gallon Definitions

In this article, we have focused on converting imperial gallons to litres. However, it’s important to note there are several other types of gallons in use as well.

US Gallon

The US gallon, used in the United States, is smaller than the imperial gallon at 3.78541 litres. Be careful not to confuse US gallons with imperial gallons during conversion.

Dry Gallon

The dry gallon was used in the UK for measuring dry goods like grain or cement. Its definition has varied over time, but often approximated 4.405 litres.

Wine Gallon

The wine gallon was used for tax purposes on alcoholic beverages. Its value was based on the volume occupied by 8 troy pounds of wine. The wine gallon is approximately 3.785 litres.

There were also many local gallon variants used in trades like beer or cider. So be sure to determine which type of gallon is implied in any conversion to avoid mistakes.

Converting Gallons to Other Units

We’ve focused on converting between imperial gallons and litres, but you can use the same approach to convert gallons to other metric units like millilitres, cubic metres, etc.

Some examples:

  • 1 gallon = 4.54609 litres = 4546.09 millilitres
  • 10 gallons = 45.4609 litres = 0.04546 cubic metres

And starting from other units:

  • 2500 ml = 2.5 litres = 0.55119 gallons
  • 0.01 cubic metres = 10 litres = 2.19969 gallons

The conversion factors we’ve discussed can be applied regardless of the metric unit involved. The key is converting everything to fundamental units like litres or cubic metres first.


We’ve covered a lot of ground explaining how many litres there are in a British gallon. Here are the key points:

  • One imperial gallon equals exactly 4.54609 litres.
  • This standard value was established in 1824 based on the gallon containing 10 pounds of water.
  • The simple conversion factor allows easy calculation between gallons and litres.
  • Rough conversion is also easy – 4.5 litres per gallon, 0.22 gallons per litre.
  • Take care to distinguish imperial gallons from other types like US gallons.
  • The gallon-litre conversion can assist with practical tasks like cooking, fuel usage estimation and more.

So in summary, the answer to our original question is:

There are 4.54609 litres in every 1 imperial gallon.

We hope this explanation has made the gallon-litre conversion clear. Knowing this relationship can help with many measurement situations involving British gallons and metric litres.

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