Litres, Gallons, Pints and Cups: Understanding Volume Units

By ConvertStuffNow  ·  7 min read

Volume units are some of the most confusing in everyday life — not because the conversions are particularly complex, but because the same name often means two different things depending on where you are. A pint in the UK is 568 ml. A pint in the US is 473 ml. You can order a pint of beer on both sides of the Atlantic, but you'll get a noticeably different amount.

This guide explains the most common volume units, where they're used, and how to convert between them — with particular attention to the differences that actually catch people out.

The metric system: litres and millilitres

Litres and millilitres are the standard volume units in most of the world. A litre is 1,000 millilitres. The relationships within the metric system are clean:

• 1 litre (L) = 1,000 millilitres (ml)
• 1 centilitre (cl) = 10 ml (wine glasses in restaurants often use centilitres)
• 1 decilitre (dl) = 100 ml (used in some Scandinavian recipes)

One litre of water weighs almost exactly 1 kilogram at room temperature (it's 0.9998 kg to be precise). This is by design — the litre was originally defined in relation to the kilogram. It makes for a handy cross-unit reference when working with water-based liquids.

The gallon problem: US vs Imperial

The gallon is where things get complicated. There are two different gallons:

The US gallon: 3.78541 litres. Used in the United States for fuel, beverages and large liquid quantities.

The Imperial (UK) gallon: 4.54609 litres. Originally defined as 10 pounds of water. Still used in the UK for fuel economy (mpg) even though petrol is sold by the litre.

The US gallon is about 83% of the Imperial gallon. A 5-gallon water jug in the US holds about 18.9 litres; a 5-gallon container in a UK context would hold about 22.7 litres. This difference matters for fuel economy comparisons — a car that does 40 mpg (US) does about 48 mpg (Imperial), because the Imperial gallon is larger.

The pint: again, two different things

Pints follow the same split:

• US pint: 473 ml (one-eighth of a US gallon)
• Imperial pint: 568 ml (one-eighth of an Imperial gallon)

A UK pint of beer is 568 ml. A US pint glass at many bars is 473 ml. If a British person orders "a pint" in the US, they're getting roughly 17% less than they expect. In recipes, "1 pint of milk" means different amounts in US and UK cookbooks.

Fluid ounces: also two different sizes

A US fluid ounce is 29.57 ml. A UK (Imperial) fluid ounce is 28.41 ml. The difference is small — about 4% — but across large quantities it adds up. There are 20 Imperial fluid ounces in an Imperial pint; there are 16 US fluid ounces in a US pint.

Cups: mainly a cooking unit

The cup is a cooking measurement used primarily in the United States, Australia, Canada and New Zealand. It's not a legal unit of measurement but it's extremely common in recipes. The values:

• US cup: 236.59 ml (approximately 237 ml)
• Metric cup (Australia, Canada, NZ): exactly 250 ml

For most cooking purposes the difference between 237 ml and 250 ml is small enough not to matter. For baking, where precision is more important, it can affect results — see our article on cooking with foreign recipes for more detail on this.

Full conversion table: all common volume units

Fuel: litres per 100 km vs miles per gallon

Fuel consumption adds another layer of confusion because the two systems measure efficiency in opposite ways. Litres per 100 km (L/100km) — used in most metric countries — measures how much fuel you need. Lower is better. Miles per gallon (mpg) — used in the US and UK — measures how far you can go on a fixed amount of fuel. Higher is better.

You can't simply convert between them by multiplying — you have to use a reciprocal formula. The approximate conversion for US mpg: divide 235 by the L/100km value. So a car using 8 L/100km does approximately 235 ÷ 8 ≈ 29 mpg (US). For Imperial mpg, divide 282 by the L/100km value.

Quick kitchen reference

All conversion values are based on internationally recognised definitions. US customary and Imperial units differ — check which system a recipe or specification uses before converting.