Imperial units From Wikipedia, the free encyclopedia Jump to: navigation, search This article is about the post-1824 measures used in the British Empire and countries in the British sphere of influence. For the units used in England before 1824, see English units. For the system of weight, see Avoirdupois. For United States customary units, see Customary units . Imperial units or the imperial system is a system of units, first defined in the British Weights and Measures Act of 1824, later refined (until 1959) and reduced. The system came into official use across the British Empire. By the late 20th century most nations of the former empire had officially adopted the metric system as their main system of measurement. The former Weights and Measures office in Seven Sisters, London. Contents [hide] • 1 Relation to other systems • 2 Units ○ 2.1 Length ○ 2.2 Area ○ 2.3 Volume 2.3.1 British apothecaries ' volume measures ○ 2.4 Mass • 3 Current use of imperial units ○ 3.1 United Kingdom ○ 3.2 Canada ○ 3.3 Australia ○ 3.4 Republic of Ireland ○ 3.5 Other countries • 4 See also • 5 References • 6 External links [edit] Relation to other systems The imperial system is one of many systems of English or foot-pound-second units, so named because of the base units of length, mass and time. Although most of the units are defined in more than one system, some subsidiary units were used to a much greater extent, or for different purposes, in one area rather than the other. The distinctions between these systems are often not drawn precisely. One such system is the US customary system, which is historically derived from units which were in use in England at the time of settlement. Because the United States was already independent at the time, these units were unaffected by the introduction of the imperial system. Units of length and area are mostly shared between the imperial and US systems, albeit being partially and temporarily defined differently. Capacity measures differ the most due to the introduction of the imperial gallon and the unification of wet and dry measures. The avoirdupois system applies only to weights; it has a long designation and a short designation for the hundredweight and ton. Another distinction to be noted is that between these systems and older British/English units/systems or newer additions. The term imperial should not be applied to English units that were outlawed in the Weights and Measures Act 1824 or earlier, or which had fallen out of use by that time, nor to post-imperial inventions such as the slug or poundal. [edit] Units [edit] Length Imperial standards of length 1876 in Trafalgar Square, London. Since 1959, the US and the British yard have been defined identically to be 0.9144 metres, to match the international yard.[citation needed] Metric equivalents in this article usually assume this latest official definition. Before this date, the most precise measurement of the Imperial Standard Yard was 0.914398416 metres.[1] Table of length equivalent units Relative to Unit Feet Millimetres Metres Notes previous 0.000 025 thou (th) 1⁄ 0.0254 25.4 μm 12000 4 1 inch (in) 1000 thous ⁄12 25.4 0.025 4 foot (ft) 12 inches 1 304.8 0.3048 yard Defined as exactly 0.9144 metres 3 feet 3 914.4 0.9144 (yd) since 1959 The British Admiralty in practice used a fathom as 6 feet. This was despite 1 its being ⁄1000 of a nautical mile (i.e. 6.08 feet) until the adoption of the international nautical mile. The commonly accepted definition of a fathom was always 6 feet. The fathom 2 yards 6.08 or 6[2] 1,853.184 1.853184conflict was inconsequential as (ftm) Admiralty nautical charts designated depths shallower than 5 fathoms in feet on older imperial charts. Today all charts worldwide are metric, except for USA Hydrographic Office charts, which use feet for all depth ranges. chain 11 fathoms 66 20116.8 20.1168 (Ch) furlong 10 chains 660 201.168 (fur) mile 8 furlongs 5,280 1,609.344 (mi) league No longer an official unit in any 3 miles 15,840 4,828.032 (Lea) nation. Maritime units cable ~100 fathoms 608 185.3184One tenth of a nautical mile. When in use it was approximated colloquially as 100 fathoms. nautical 10 cables 6,080 1,853.184Used to measure distances at sea. mile Until the adoption of the international definition of 1852 metres in 1970, the British nautical (Admiralty) mile was defined as 6,080 feet. It was not readily expressible in terms of any of the intermediate units, because it was derived from the circumference of the Earth (like the original metre). Gunter's survey units (17th century onwards) 66 link ⁄100 201.168 0.2011687.92 inches 66 rod 25 links ⁄4 5,029.2 5.0292The rod is also called pole or perch. 1 chain 4 poles 66 20.1168 ⁄10 furlong [edit] Area Area Relation Square Square Square Unit to units of Square metres Hectares Notes feet rods miles length Although the proper term is square rod, for centuries this unit has 1 rod × 1 perch 272.25 1 1⁄ 25.29285264 0.002529been called a pole or rod 102400 perch or, more properly square pole or square perch. 1 furlong × The rood is also called a rood 10,890 40 1⁄ 1,011.7141056 0.1012 1 rod[3] 2560 rod.[4][5] 1 furlong × acre 43,560 160 1⁄ 4,046.8564224 0.4047 1 chain 640 Note: All equivalences are exact except the hectares, which are accurate to four significant figures. [edit] Volume In 1824, the United Kingdom adopted a close approximation to the ale gallon known as the imperial gallon. The imperial gallon was based on the volume of 10 lb of distilled water weighed in air with brass weights with the barometer standing at 30 in Hg at a temperature of 62 °F. In 1963 this definition was refined as the space occupied by 10 lb of distilled water of density 0.998859 g/ml weighed in air of density 0.001217 g/ml against weights of density 8.136 g/ml. This works out to 4.545096 l, or 277.420 cu in. The Weights and Measures Act of 1985 switched to a gallon of exactly 4.54609 l (approximately 277.4 cu in).[6] Table of volume units Imperial Cubic Unit Imperial pint Millilitres US ounces US pints ounce inches fluid ounce 1 1⁄ 28.4130625 1.7339 0.96076 0.060047 (fl oz) 20 1 gill (gi) 5 ⁄4 142.0653125 8.6694 4.8038 0.30024 pint (pt) 20 1 568.26125 34.677 19.215 1.2009 quart (qt) 40 2 1,136.5225 69.355 38.430 2.4019 gallon (gal) 160 8 4,546.09 277.42 153.72 9.6076 Note: The millilitre equivalences are exact whereas the conversions to cubic-inch and US measures are correct to five significant figures. [edit] British apothecaries' volume measures Table of British apothecaries' volume units[7] Unit Previous Unit Metric Value minim ... 59.1938802 µL fluid scruple 20 minims 1.1838776 mL fluid drachm 3 fluid scruples 3.5516328 mL fluid ounce 8 fluid drachms 28.4130625 mL pint 20 fluid ounces 568.26125 mL gallon 8 pints 4.54609 L [edit] Mass In the 19th and 20th centuries the UK has used three different systems for mass and weight:[8] • troy weight , used for precious metals; • avoirdupois weight, used for most other purposes; and • apothecaries ' weight , now virtually unused since the metric system is used for all scientific purposes. The troy pound (373.2417216 g) was made the primary unit of mass by the 1824 Act; however, its use was abolished in the UK on 6 January 1879, making the Avoirdupois pound the primary unit of mass with only the troy ounce (31.1034768 g) and its decimal subdivisions retained. In all the systems, the fundamental unit is the pound, and all other units are defined as fractions or multiples of it. Table of mass units Unit Pounds Grams Kilograms Notes 1 grain (gr) ⁄7000 0.06479891 Exactly 64.79891 milligrams. 1 drachm (drc) ⁄256 1.7718451953125 1 ounce (oz) ⁄16 28.349523125 Exactly 453.59237 grams by pound (lb) 1 453.59237 0.45359237 definition. A person's weight is often quoted in stone and pounds in English-speaking countries using the avoirdupois stone (st) 14 6,350.29318 6.35029318 system, with the exception of the United States and Canada, where it is usually quoted in pounds. A "quarter" was also commonly used quarter (qtr) 28 12.70058636to refer to a quarter of a pound in a retail context. hundredweight 112 50.80234544 (cwt) 20 hundredweights in both systems, ton (t) 2240 1,016.0469088 US hundredweight being lighter. The British ton (the long ton) is 2240 pounds, which is very close to a metric tonne, whereas the ton generally used in the United States is the "short ton" of 2000 pounds (907.18474 kg). Each is divided into 20 hundredweights (cwt), the British hundredweight of 112 pounds being 12% heavier than the American hundredweight of 100 pounds. [edit] Current use of imperial units A baby bottle that measures in three measurement systems—metric, imperial (UK), and US customary. [edit] United Kingdom Main article: Metrication in the United Kingdom British law now defines each imperial unit in terms of the metric equivalent. The metric system is in official use within the United Kingdom; however, use of Imperial unit is widespread in many cases.