Defenders of the imperial system occasionally cite Americans’ continued use of non-metric measurements to justify Britain’s dual system. Ronnie Cohen is not convinced.
It has been claimed that the UK did not need change from its imperial system of measures as the USA had and still has a similar system. It is true that they use a few of the same measurement units that are still in common usage in Britain. But many features of US non-metric measurements and some aspects of their usage would be unfamiliar to most Britons. Here we take a look at the largely unknown features of US customary units that we do not see in the UK.
The UK and US use the international versions of the imperial inch, foot, yard and mile. These were standardised by six English-speaking nations on 1 July 1959 using the metric system. Before that there were slight variations of these units between these nations. Older versions of these imperial units still survive today called US survey measures and are used by the US for land measurements. These vary from the international versions of imperial distance measures by 2 parts per million. The US survey foot is defined as exactly 1200/3937 metres. The US uses the survey foot as well as the international foot of 0.3048 metres.
The US uses land area measurements called “sections of land” and “townships”. A section of land is defined as one square mile and a township is defined as 36 square miles or 36 sections of land. The British never used these terms in the context of land measurements.
The Americans use separate dry volume and liquid volume measures whereas the British used a single set of imperial measures for dry and liquid volumes.
For liquid volumes, the Americans use the gill, pint, quart and gallon. The British used imperial units with the same names but the British versions of these units are approximately 20% larger than the US versions. The British have a quart in their imperial measurement tables but it is seldom used in the UK. While the US gallon is divided into 128 fluid ounces, the British gallon is divided into 160 fluid ounces. The fluid ounce varies slightly between the UK and US. The UK fluid ounce is 28.41 mL but the US fluid ounce is 29.57 mL, about 4% larger than the UK fluid ounce.
For dry volumes, the Americans have dry pints, dry quarts, pecks and bushels. The British imperial versions of these units were approximately 3% larger than these dry measures.
For mass measurements, the US uses the short hundredweight of 100 lb and the short ton of 2000 lb. The US also recognises the gross or long measures for the hundredweight and ton, which were once used in the UK. The latter are 12% larger than the short measures.
Other US measurement units likely to be unfamiliar to Britons include:
- Measuring Cup: This is equal to exactly 8 US fluid ounces or half a US liquid pint.
- Cord: This unit is equal to exactly 128 cubic feet and used for measuring firewood.
- Board Foot or Super Foot: A measure of volume measuring 1 inch x 1 foot x 1 foot. It is used for measuring lumber.
- Pounds per Board Foot: A measurement of density related to the Board Foot.
- Acre-Foot: A volume of one acre of surface area to a depth of one foot and used for measuring large volumes of water.
- Gasoline Gallon Equivalent: A unit of volume equal to 33.7 kilowatt hours.
- Miles per Gallon Gasoline Equivalent: A fuel economy measure closely related to gasoline gas equivalent.
- US Dry Barrel: A volume equal to 7056 cubic inches.
- US Barrel for Cranberries: A volume equal to 5826 cubic inches. Yes, you read that correctly; the Americans have a barrel exclusively for cranberries!
- US Liquid Barrel: Most liquid barrels in the US contain 31.5 US gallons.
- US Beer Barrel: The US beer barrel contains 31 US gallons.
Americans normally express their weight only in pounds whereas the British tend to use a combinations of stones and pounds. The stone is absent from US measurement tables.
Americans use feet on road signs for short distances whereas the British use yards and fractions of a mile in similar circumstances.
The US still sells petrol by the US gallon – around 18% smaller than the UK gallon. So fuel consumption figures in mpg are country specific.
The next article on Metric Views will appear on 15 February and will mark an important anniversary. We shall be interested to see how this date is covered in the UK media.