US vs UK Measurements: Why a Pint Isn’t Always a Pint
Americans and Britons use many of the same unit names — pint, quart, gallon, fluid ounce, ton — yet several of them describe different amounts. Order a pint of beer in London and you receive about 20% more than a pint in New York. Fill up a car in the UK and the fuel economy in miles per gallon looks better than the same car’s figure in the US, even though nothing about the engine has changed.
The reason is history. The United States kept the English units that were in use before American independence, while Britain reformed its system in 1824. The two systems have drifted apart ever since, and knowing where they differ saves a lot of confusion in recipes, travel and online shopping.
How the two systems split
Before 1824, England had several competing gallons: a wine gallon, an ale gallon and a corn gallon among them. The American colonies inherited this mixture, and after independence the US standardised on the wine gallon of 231 cubic inches, a definition dating back to 1707 under Queen Anne. That is still the US liquid gallon today, about 3.785 litres.
Britain went a different way. The Weights and Measures Act of 1824 swept away the old gallons and replaced them with a single imperial gallon, defined as the volume of ten pounds of water under specified conditions. That works out to roughly 4.546 litres — about 20% larger than the American gallon. Every unit derived from the gallon, from the quart down to the pint, inherited that difference.
Liquid volume compared
The confusing part is the fluid ounce. The imperial fluid ounce is actually slightly smaller than the US one, yet the imperial pint is larger. That is because an imperial pint contains 20 imperial fluid ounces, while a US pint contains only 16 US fluid ounces.
| Unit | United States | United Kingdom (imperial) |
|---|---|---|
| Fluid ounce | 29.57 mL | 28.41 mL |
| Pint | 473.2 mL (16 US fl oz) | 568.3 mL (20 imp fl oz) |
| Quart | 946.4 mL | 1.137 L |
| Gallon | 3.785 L | 4.546 L |
Weight: tons, hundredweights and stones
Both countries use the same avoirdupois pound — since 1959 it has been defined internationally as exactly 0.45359237 kilograms — and the same ounce of 1/16 pound. The differences appear in the larger units built from the pound.
In the US, a hundredweight is 100 pounds and a ton (the “short ton”) is 2,000 pounds. The traditional British hundredweight is 112 pounds, and twenty of them make a “long ton” of 2,240 pounds. Neither should be confused with the metric tonne of 1,000 kilograms, which sits between the two at about 2,205 pounds.
The stone is a mostly British unit equal to 14 pounds (about 6.35 kg). It survives almost exclusively for describing body weight: a Briton is far more likely to say they weigh “11 stone 4” than “158 pounds”.
| Unit | Pounds | Kilograms |
|---|---|---|
| Stone (UK) | 14 lb | 6.35 kg |
| Hundredweight (US) | 100 lb | 45.36 kg |
| Hundredweight (UK) | 112 lb | 50.80 kg |
| Short ton (US) | 2,000 lb | 907.2 kg |
| Long ton (UK) | 2,240 lb | 1,016 kg |
| Metric tonne | 2,204.6 lb | 1,000 kg |
Miles per gallon: same car, different number
Because the imperial gallon is about 1.2 times the US gallon, a car travels further on one. A vehicle rated at 30 miles per US gallon achieves about 36 miles per imperial gallon. When you compare fuel economy figures from British and American reviews, multiply the US figure by roughly 1.2, or divide the UK figure by 1.2, before drawing conclusions.
Adding to the muddle, UK petrol stations sell fuel by the litre, while fuel economy is still commonly quoted in miles per imperial gallon. Most of continental Europe instead uses litres per 100 kilometres, where a lower number means a more efficient car.
What the UK actually uses today
Britain officially adopted metric units for most trade over several decades, but everyday life remains mixed. Road signs show distances in miles and speed limits in miles per hour. Draught beer and cider in pubs are served in pints, and doorstep milk is still sold in pints. Most other groceries are sold in grams and kilograms, and many people give their height in feet and inches and their weight in stones.
The US, by contrast, uses customary units for almost everything in daily life — road distances, recipes, body weight and temperature — while science, medicine and much of manufacturing work in metric.
Practical tips
- When a recipe says “pint”, check whether it is American or British. A British recipe calling for a pint of milk needs about 568 mL, not 473 mL.
- A British “half” of beer is half an imperial pint, about 284 mL — close to a 10 fl oz US glass.
- Online shoppers comparing liquid products should look for millilitres or litres on the label, which are identical in both countries.
- If a UK source gives your weight in stones, multiply by 14 to get pounds, then add any leftover pounds.