The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of length; both are based on the older English unit of length equal to 5,280 English feet, or 1,760 yards. The statute mile was standardised as a unit of length between the Commonwealth of Nations and the United States by an international agreement in 1959, when the yard was formally redefined with respect to SI units as 0.9144 metres, making the mile exactly 1609.344 metres (1.609344 kilometres). For everyday use, five miles equates roughly to eight kilometres. Mileage is the term used informally for a distance expressed in miles. With qualifiers, mile is also used to describe or translate a wide range of units derived from or roughly equivalent to the Roman mile (roughly 1.48 km), 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 pedes (lit. 'feet'), but the greater importance of furlongs in the Elizabethan-era 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 across the British Empire, some successor states 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, although it was officially phased out in 2022. While most countries replaced the mile with the kilometre when switching to the International System of Units (SI), the international mile continues to be used in some countries, such as 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.
Name 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 the nominal ellipsis form of mīlle passus 'mile' or mīlia passuum 'miles', 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, statute mile may refer to the present international mile or to any other form of English mile since an act of Parliament, the Restriction on Building Act 1592 (35 Eliz. 1. c. 6) was passed in 1593, which set it as a distance of 1,760 yards. Under American law, however, 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.
Abbreviation The mile has been variously abbreviated in English—with and without a trailing period—as "mi", "M", "ml", and "m". The American National Institute of Standards and Technology now uses and recommends "mi" 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 an initialism as in "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 symbol 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 spelt out in all cases.
Historical
Roman
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 distance was indirectly standardised by Agrippa's establishment of a standard Roman foot in 29 BC, and the definition of a pace as 5 (Roman) feet. An Imperial Roman mile thus denoted 5,000 Roman feet. Surveyors and specialised 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 1,479 metres (4,854 ft; 0.919 miles) in length, slightly less than the 1,610 metres (5,280 ft) of the modern international mile. In Hellenic areas of the Empire, the Roman mile (Ancient Greek: μίλιον, mílion) was used beside the native Greek units as equivalent to 8 stadia of 600 Greek feet. The mílion continued to be used as a Byzantine unit and was also used as the name of the zero mile marker for the Byzantine Empire, the Milion, located at the head of the Mese near Hagia Sophia. The Roman mile spread throughout Europe, with its local variations giving rise to the different size units. Also arising from the Roman mile is the milestone. All roads radiated out from the Roman Forum throughout the Empire – 50,000 (Roman) miles of stone-paved roads. At every mile was placed a shaped stone. Originally, these were obelisks made from granite, marble, or whatever local stone was available. On these was carved a Roman numeral, indicating the number of miles from the centre of Rome – the Forum. Hence, one can know how far one is from Rome.
Ptolemaic mile In the 2nd-century, Greco-Roman polymath, Claudius Ptolemy, of Alexandria (Egypt), in his Almagest and Geography, defined a mile as a geographic arcminute of longitude, of the earth's circumference, equivalent to 1:60 of a degree of longitude, or 1:21,600 of the circumference. While his estimate of the circumference of the earth, and therefore the derived length of a stade, and a mile, from third party observations, principally offered in non-normalised stadion (600 Greek feet), Egyptian schoinos, and Persian parasang were erroneous. Ptolemy's assumptions of a customary stade to be 1/8 of a Roman mile, 1/30 of a schoinos or parasang, 1/500 of an arc-minute, or ~185 metres, his Geographical mile, is the basis of the current nautical mile, and was adopted by medieval Arab and European cartographers.
Arabic
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