Order a pint in a London pub and you get 568 ml of beer. Order a pint in New York and you get about 473 ml. Both are called a pint, both are legal, and they are not the same size. The same is true of the gallon, the quart and the fluid ounce. If you follow an American recipe in Britain, compare fuel economy between countries, or read an old Canadian car manual, the difference matters.
Why there are two systems
Before 1824, Britain used several different gallons for wine, ale and corn. The United States kept the old wine gallon of 231 cubic inches. Britain replaced all of them in 1824 with the new imperial gallon, defined from the volume of 10 pounds of water. The two systems have been separate ever since, and today both are defined exactly in litres.
The exact sizes
| Unit | US customary | UK imperial |
|---|---|---|
| Gallon | 3.785411784 L | 4.54609 L |
| Quart (1/4 gallon) | 946.353 ml | 1,136.52 ml |
| Pint (1/8 gallon) | 473.176 ml | 568.261 ml |
| Fluid ounce | 29.5735 ml | 28.4131 ml |
| Fluid ounces in a pint | 16 | 20 |
| Fluid ounces in a gallon | 128 | 160 |
Two things stand out. The imperial gallon, quart and pint are about 20% larger (exactly 1.20095 times). But the US fluid ounce is about 4% larger than the imperial one. The UK pint is bigger because it holds 20 smaller ounces, while the US pint holds 16 larger ones.
Quick conversions
- US gallons to litres: multiply by 3.785
- UK gallons to litres: multiply by 4.546
- US gallons to UK gallons: multiply by 0.8327
- UK gallons to US gallons: multiply by 1.2009
- US pints to UK pints: multiply by 0.8327
Worked example: a US recipe needs 2 US quarts of stock. 2 × 946.353 = 1,892.7 ml, so use about 1.9 litres, not 2.27 litres (which is 2 UK quarts).
Cups and spoons in recipes
Cups are where most kitchen mistakes happen, because there are three common cups:
| Cup | Volume | Where it is used |
|---|---|---|
| US customary cup | 236.6 ml | Most American recipes |
| US legal cup | 240 ml | US nutrition labels |
| Metric cup | 250 ml | Canada, Australia, New Zealand |
For most baking, the 6% gap between 236.6 ml and 250 ml will not ruin a cake, but it adds up in recipes that use 3 or 4 cups of flour or liquid. A US tablespoon is 14.79 ml and a US teaspoon is 4.93 ml, while UK and metric spoons are 15 ml and 5 ml, which is close enough to treat as equal.
Tip: for baking, weigh dry ingredients in grams where possible. A cup of flour can weigh anywhere from 120 g to 150 g depending on how it is scooped.
Fuel economy: miles per gallon is not the same everywhere
Because the gallons differ, a car rated at 40 mpg in the UK is only about 33 mpg in US terms. To compare cars fairly, convert both to litres per 100 km:
- L/100 km = 235.215 ÷ mpg (US)
- L/100 km = 282.481 ÷ mpg (UK)
Worked example: 40 mpg (UK) = 282.481 ÷ 40 = 7.06 L/100 km. 40 mpg (US) = 235.215 ÷ 40 = 5.88 L/100 km. The US figure means a more efficient car.
Canada sells fuel by the litre and rates cars in L/100 km, but many Canadians still quote imperial mpg, so check which gallon a figure uses.
Common mistakes
- Assuming a pint is a pint. Always check whether a source is American or British.
- Converting fluid ounces the wrong way round. 10 US fl oz is 295.7 ml, but 10 UK fl oz is 284.1 ml.
- Using the US cup for Canadian or Australian recipes. Those use the 250 ml metric cup.
Convert any volume
Our volume converter covers US and imperial gallons, quarts, pints, cups, fluid ounces, tablespoons and teaspoons, with the formula shown for each pair.
Frequently asked questions
Is a UK pint bigger than a US pint? Yes. A UK pint is 568.261 ml and a US pint is 473.176 ml, so the UK pint is about 20% bigger.
How many litres are in a gallon? 3.785 litres in a US gallon and 4.546 litres in a UK (imperial) gallon.
Does Canada use US or imperial gallons? Historically imperial, but Canada now uses litres officially. Older Canadian sources quoting gallons usually mean imperial gallons.
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