Volume Converter

How to use the volume converter

1. Enter the amount in Value, then choose the unit you have in From and the unit you want in To.
2. Check whether the unit is a US or a UK one. The two countries use the same names for different sizes, so each is listed separately with the country in its name.
3. Read the answer and then scan the table below it for the same volume in every other unit. Each row has its own Copy button.

All factors are exact definitions, not rounded approximations, so a chain of conversions gives the same answer however you go.

US gallon, UK gallon and why they differ

The US gallon is defined as exactly 231 cubic inches, which is 3.785411784 litres. It comes from the old English wine gallon. The UK, or imperial, gallon was defined in 1824 as the volume of 10 pounds of water and later fixed at exactly 4.54609 litres. The imperial gallon is therefore about 20% larger (a ratio of 1.2009), and the difference carries through to every unit built on it.

Notice the fluid ounce: the US one is slightly larger than the UK one, yet a UK pint is bigger because it holds 20 fluid ounces against the US pint's 16. This is why a "pint" of beer in London is not the same as a pint in New York, and why fuel economy figures in miles per gallon differ between the countries. A car rated at 35 mpg on the UK scale is only 29.1 mpg on the US scale, since each UK gallon is larger.

Cooking measures

Many countries outside the US, including Australia, Canada, New Zealand and South Africa, use a metric cup of 250 mL and a tablespoon of 15 to 20 mL, so a recipe written there will not match a US cup of 236.6 mL. Australia's tablespoon is 20 mL, for example, while the US one is 14.8 mL. For baking, where proportions matter, measure by weight when you can, or check which cup the recipe means.

Worked examples

• A 12 US gallon fuel tank in litres: 12 × 3.785411784 = 45.425 L.
• The same 12 gallons, if they were imperial: 12 × 4.54609 = 54.553 L, which is 9.1 litres more.
• A 2-litre bottle in US cups: 2 ÷ 0.2365882365 = 8.454 cups.
• A 1 m × 1 m × 1 m tank in litres: 1 cubic metre is exactly 1,000 litres.
• A 568 mL milk bottle: the traditional UK pint, 568.26 mL, equals 20 UK fluid ounces and about 19.2 US fluid ounces.

Formula

result = value × (litres per source unit) ÷ (litres per target unit)

Litres are the middle step. A litre is defined as exactly one cubic decimetre (1,000 cm³), so 1 mL equals 1 cm³ and 1 m³ equals 1,000 L. Volume is length cubed, which is why a cubic foot (28.316846592 L) is 0.3048³ cubic metres, and why doubling every side of a box gives eight times the volume.

Fuel economy and tank sizes

Metric fuel economy counts litres used per distance, so a smaller number is better, while mpg counts distance per volume, so a larger number is better. To convert, divide 235.215 by the L/100 km figure for US mpg, or 282.481 for UK mpg. A car using 8 L/100 km does 29.4 mpg by US gallons and 35.3 mpg by imperial gallons. When you compare cars from different sources, check which gallon the mpg figure uses before deciding one is more efficient.

Accuracy and limits

All the factors are exact international or legal definitions, so results are exact to the digits shown. The converter measures volume, not weight: a litre of water weighs about 1 kg, but a litre of oil or honey does not. For cooking by weight, you need the density of the ingredient, which differs for every food. Dry measures such as the US bushel are not included.

Frequently asked questions