Mile

The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959. The mile is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959. With qualifiers, 'mile' is also used to describe or translate a wide range of units derived from or roughly equivalent to the Roman mile, such as the nautical mile (now 1.852 km exactly), the Italian mile (roughly 1.852 km), and the Chinese mile (now 500 m exactly). The Romans divided their mile into 5,000 roman feet but the greater importance of furlongs in pre-modern England meant that the statute mile was made equivalent to 8 furlongs or 5,280 feet in 1593. This form of the mile then spread to the British-colonized nations some of which continue to employ the mile. The US Geological Survey now employs the metre for official purposes but legacy data from its 1927 geodetic datum has meant that a separate US survey mile (6336/3937 km) continues to see some use. While most countries replaced the mile with the kilometre when switching to the International System of Units, the international mile continues to be used in some countries, such as Liberia, the United Kingdom, the United States, and a number of countries with fewer than one million inhabitants, most of which are UK or US territories, or have close historical ties with the UK or US. The mile was usually abbreviated m. in the past but is now sometimes written as mi to avoid confusion with the SI metre. However, derived units, such as miles per hour or miles per gallon, continue to be universally abbreviated as mph and mpg, respectively. The modern English word mile derives from Middle English myle and Old English mīl, which was cognate with all other Germanic terms for 'miles'. These derived from apocopated forms of the Latin mīlia or mīllia, the plural of mīle or mīlle, literally 'thousand' but used as a clipped form of mīlle passus or passuum, the Roman mile of one thousand paces. The present international mile is usually what is understood by the unqualified term 'mile'. When this distance needs to be distinguished from the nautical mile, the international mile may also be described as a 'land mile' or 'statute mile'. In British English, the 'statute mile' may refer to the present international miles or to any other form of English mile since the 1593 Act of Parliament, which set it as a distance of 1,760 yards. Under American law, however, the 'statute mile' refers to the US survey mile. Foreign and historical units translated into English as miles usually employ a qualifier to describe the kind of mile being used but this may be omitted if it is obvious from the context, such as a discussion of the 2nd-century Antonine Itinerary describing its distances in terms of 'miles' rather than 'Roman miles'. The mile has been variously abbreviated—with and without a trailing period—as m, M, ml, and mi. The American National Institute of Standards and Technology now uses and recommends mi in order to avoid confusion with the SI metre (m) and millilitre (ml). However, derived units such as miles per hour or miles per gallon continue to be abbreviated as mph and mpg rather than mi/h and mi/gal. In the United Kingdom road signs use m as the abbreviation for mile though height and width restrictions also use m as the abbreviation for the metre, which may be displayed alongside feet and inches. The BBC style holds that 'There is no acceptable abbreviation for 'miles'' and so it should be spelled out when used in describing areas. The Roman mile (mille passus, lit. 'thousand paces'; abbr. m.p.; also milia passuum and mille) consisted of a thousand paces as measured by every other step—as in the total distance of the left foot hitting the ground 1,000 times. The ancient Romans, marching their armies through uncharted territory, would often push a carved stick in the ground after each 1,000 paces. Well-fed and harshly driven Roman legionaries in good weather thus created longer miles. The distance was indirectly standardised by Agrippa's establishment of a standard Roman foot (Agrippa's own) in 29 BCE, and the definition of a pace as 5 feet. An Imperial Roman mile thus denoted 5,000 Roman feet. Surveyors and specialized equipment such as the decempeda and dioptra then spread its use. In modern times, Agrippa's Imperial Roman mile was empirically estimated to have been about 1,617 yards (1,479 m) in length.