An American walks into a pub in London and orders a pint. It looks similar, but, given the amount of the golden-brown, oddly warm liquid sloshing around in the glass vessel, it almost seems to be a little too much.
This is because a pint in the United Kingdom is bigger than a pint in the United States. The UK pint is 20 fluid ounces, while the US pint fills up 16 fl oz. However, this translation is not that simple, as fluid ounces do not equal one another across the Atlantic. Here is the breakdown of volume between the two countries:
- The British Imperial fluid ounce is equal to 28.413 milliliters, while the US Customary fluid ounce is 29.573 ml.
- The British Imperial pint is 568.261 ml (20 fluid ounces), while the US Customary pint is 473.176 ml (16 fl oz).
- The British Imperial quart is 1.13 liters (40 fl oz), while the US Customary quart is 0.94 L (32 fl oz).
- The British Imperial gallon is 4.54 L (160 fl oz), while the US Customary gallon is 3.78 L (128 fl oz).
Background of English Units
At the root of this divide is the difference in measurement systems. While the American system of measurement often is referred to as the Imperial System, this usage is erroneous. The US, ever since the formative years of the New World-nation, has used the US Customary System. The Imperial System, alternatively, was established in 1824 for Great Britain and its colonies. Even today, decades after officially switching to SI (metric) units, volume in the UK is measured in British Imperial units.
Both these systems, however, derived from English units. English units were in use until the early 1800s, and they saw a vast range of influences due to the frenzied history of the British Isles. This historical precedence spanned a millennium, so, to keep things short: the Celtic Britons lived in modern-day Britain, and they were at war with Roman invaders for the first few centuries AD. After the Romans left, the Celts were invaded and displaced by the Anglo-Saxons, who were dominated by the Normans.
This resulted in a plethora of units of measurement. Many Anglo-Saxon units had some basis in the people’s agricultural past. For example, 3 barleycorns equaled 1 ynce (inch), and an acre was considered a field the size a farmer could plow in a single day. The foot, obviously having a connection to the length of the human appendage, was in use, but it had various conflicting specifications.
The Norman kings brought Roman measurements to Britain, specifically the 12-inch foot and the mile, which was defined originally as the length of 1000 paces of a Roman legion. If you’d like to read more about this background, please refer to our article on the History of the US Customary System.
Differences Between US Customary and Imperial Units
By the time of the American Revolution, English units were diverse but active. However, the newly-independent American Colonies experienced influences not only from the Anglo-Saxons, the Normans, and the Romans, but also from past colonists from Holland, France, and Spain. This necessitated the birth of the US Customary System in the united colonies. Decades later, in 1824, Great Britain established the Imperial System.
This initiated the divide between the two systems of measurement. Nonetheless, US Customary and Imperial units were, and still remain, mostly the same. However, an American fluid ounce was defined originally as the volume occupied by an ounce of wine, while the Imperial fluid ounce was defined as the volume occupied by an ounce of water. This made the US Customary fluid ounce a little larger, since alcohol is less dense than water.
Furthermore, the Mendenhall Order of 1893 defined the US units in terms of metric units, removing any direct relationship between US Customary and Imperial volume units of the same name.
Other than volume, there are a few variations between US Customary and Imperial units. Dry volume, for example, is measured differently than liquid volume in both systems. An Imperial bushel is equal to 36.369 liters, while a US dry bushel is equal to 35.239 L.
In addition, the hundredweight varies between the US Customary and Imperial Systems. Since a ton is always equal to 20 hundredweight, the British Imperial ton is 2240 pounds (long ton) and the US ton is 2000 lbs (short ton).