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Both the imperial and United States customary systems of measurement derive from earlier English systems used in the Middle Ages, that were the result of a combination of the local Anglo-Saxon units inherited from German tribes and Roman units brought by William the Conqueror after the Norman Conquest of England in 1066. Having this shared heritage, the two systems are quite similar, but there are differences. The US customary system is based on English systems of the 18th century, while the Imperial system was defined in 1824, after American independence. ==Volume== Volume may be measured either in terms of units of cubic length or with specific volume units. The units of cubic length (the cubic inch, cubic foot, cubic mile, etc.) are the same in the imperial and US customary systems but with the specific units of volume (the bushel, gallon, fluid ounce, etc.) they differ. The US customary system has one set of units for fluids and another set for dry goods. The imperial system has only one set defined independently of and subdivided differently from its US counterparts. By the end of the eighteenth century various systems of volume measurement were in use throughout the British Empire. Wine was measured with units based on the Queen Anne's gallon of 231 cubic inches (3.785 L). Beer was measured with units based on an ale gallon of 282 cubic inches (4.621 L). Grain was measured with the Winchester measure with a gallon of approximately 268.8 cubic inches (one eighth of a Winchester bushel or 4.405 L). In 1824 these were replaced with a single system based on the imperial gallon.〔Wine gallons, however, continued to be used for tax purposes in the UK until the late 1990s.〕 Originally defined as the volume of of distilled water (under certain conditions),〔The water was to be weighed in air with brass weights with the barometer standing at at a temperature of . In 1963 these conditions were redefined such that the water was to have a density of and to be weighed in air of density against weights of density 8.136 g/mL.〕 then redefined by The Weights and Measures Act of 1985 to be exactly (277.4 cu in), the imperial gallon is close in size to the old ale gallon. The Winchester measure was made obsolete in the British Empire but remained in use in the US.〔Originally defined as the volume of a cylinder in diameter and deep, the Winchester bushel was redefined in the US as cubic inches.〕 The Winchester bushel was replaced with an imperial bushel of 8 imperial gallons. The subdivisions of the bushel were maintained. As with US dry measures the imperial system divides the bushel into 4 pecks, 8 gallons, 32 quarts or 64 pints. Thus all of these imperial measures are about 3% larger than their US dry measure counterparts. Fluid measure is not as straightforward. The American colonists adopted a system based on the 231-cubic-inch wine gallon for all fluid purposes. This became the US fluid gallon. Both the imperial and US fluid gallon are divided into 4 quarts, 8 pints or 32 gills.〔The gill is no longer in common use.〕 However, whereas the US gill is divided into 4 US fluid ounces, the imperial gill is divided into 5 imperial fluid ounces. So whilst the imperial gallon, quart, pint and gill are about 20% larger than their US fluid measure counterparts, the fluid ounce is about 4% smaller.〔The now rarely used apothecaries' system of fluid measures further divides the fluid ounce into 8 fluid drams or 480 minims. Also in the imperial system there is a fluid scruple of 20 minims which is absent from the US customary system. Like the fluid ounce the dram and minim are about 4% smaller in the imperial system.〕 Note that one avoirdupois ounce of water has an approximate volume of one imperial fluid ounce at 62 °F (16.67 °C).〔160 imperial fluid ounces is equivalent to one imperial gallon, which is the approximate volume of 10 pounds or 160 avoirdupois ounces of water at 62 °F.〕 This convenient fluid-ounce-to-avoirdupois-ounce relation does not exist in the US system. One noticeable comparison between the imperial system and the US system is between some Canadian and American beer bottles. Many Canadian brewers package beer in an 12-imperial-fluid-ounce bottles, which are 341 mL each. American brewers package their beer in 12-US-fluid-ounce bottle, which are 355 mL each. This results in the Canadian bottles being labelled as 11.5 fl oz in US units when imported into the United States. Because Canadian beer bottles predate the adoption of the Metric System in that country, they are still sold and labelled in Canada as 341 mL. Canned beer in Canada is sold and labelled in 355 mL cans, and when exported to the US are labelled as 12 fl oz. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Comparison of the imperial and US customary measurement systems」の詳細全文を読む スポンサード リンク
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