Mile
The modern English word mile derives from Middle English and Old English, which was cognate with all other Germanic terms for miles. These derived from the nominal ellipsis form of 'mile' or 'miles', the Roman mile of one thousand paces. The Roman mile consisted of a thousand paces as measured by every other step. This meant the total distance of the left foot hitting the ground 1,000 times. Surveyors and specialized equipment such as the decempeda and dioptra then spread its use. Agrippa established a standard Roman foot in 29 BC to indirectly standardize this distance. An Imperial Roman mile thus denoted 5,000 Roman feet. In modern times, Agrippa's Imperial Roman mile was empirically estimated to have been about 1480 meters in length. This is slightly less than the 1609 meters of the modern international mile. In Hellenic areas of the Empire, the Roman mile was used beside native Greek units as equivalent to 8 stadia of 600 Greek feet. The continued use of these units persisted through Byzantine times.
The English statute mile was established by a Weights and Measures Act of Parliament in 1593 during the reign of Queen Elizabeth I. The act on the Composition of Yards and Perches had shortened the length of the foot and its associated measures. This caused the two methods of determining the mile to diverge. Owing to the importance of the surveyor's rod in deeds and surveying undertaken under Henry VIII, decreasing the length of the rod would have amounted to a significant tax increase. Parliament instead opted to maintain the mile of 8 furlongs. They increased the number of feet per mile from the old Roman value. The applicable passage of the statute reads: A Mile shall contain eight Furlongs, every Furlong forty Poles, and every Pole shall contain sixteen Foot and half. The statute mile therefore contained 5,280 feet or 1,760 yards. The distance was not uniformly adopted. Robert Morden had multiple scales on his 17th-century maps which included continuing local values. His map of Hampshire bore two different miles with a ratio of 1.14. His map of Dorset had three scales with a ratio of 1.15. In both cases, the traditional local units remained longer than the statute mile.
The Breslau mile used in Breslau and from 1630 officially in all of Silesia is equal to 11,250 ells. This measures about 6,700 meters. The Breslau mile equaled the distance from the Piaskowa Gate all the way to Psie Pole. By rolling a circle with a radius of 5 ells through Piaskowa Island, Ostrów Tumski and suburban tracts, passing eight bridges on the way, the standard Breslau mile was determined. The Croatian mile first devised by the Jesuit Stjepan Glavač on a 1673 map is the length of an arc of the equator subtended by 1 degree or 11.13 km exactly. The Danish mile following its standardization by Ole Rømer in the late 17th century was precisely equal to the Prussian mile. These were sometimes treated as equivalent to 7.5 km. Earlier values had varied: the old Danish mile had been 11.13 km. The Dutch mile has had different definitions throughout history. One of the older definitions was 5,600 ells. But the length of an ell was not standardized. So that the length of a mile could range between 3,280 m and 4,280 m. In the sixteenth century, the Dutch had three different miles: small, medium, and large.
The international mile is precisely equal to 1609.344 meters. It was established as part of the 1959 international yard and pound agreement reached by the United States, the United Kingdom, Canada, Australia, New Zealand, and the Union of South Africa. This resolved small but measurable differences that had arisen from separate physical standards each country had maintained for the yard. As with the earlier statute mile, it continues to comprise 1,760 yards or 5,280 feet. The difference from the previous standards was 2 ppm, or about 3.2 millimeters per mile. The US standard was slightly longer and the old Imperial standards had been slightly shorter than the international mile. When the international mile was introduced in English-speaking countries, the basic geodetic datum in America was the North American Datum of 1927. This had been constructed by triangulation based on the definition of the foot in the Mendenhall Order of 1893. That order defined 1 foot as approximately 0.304800609601 meters.
The US survey mile is 5,280 US survey feet, or 1,609.347 meters. Both are very slightly longer than the international mile and international foot. In the United States, the term statute mile formally refers to the survey mile. But for most purposes, the difference of less than 3 millimeters between the survey mile and the international mile is insignificant. One international mile is 0.999998 US survey miles. So statute mile can be used for either. But in some cases, such as in the US State Plane Coordinate Systems which can stretch over hundreds of miles, the accumulated difference can be significant. It is important to note that the reference is to the US survey mile. The United States redefined its yard in 1893. This resulted in US and Imperial measures of distance having very slightly different lengths. In October 2019, US National Geodetic Survey and National Institute of Standards and Technology announced their joint intent to retire the US survey foot and US survey mile. This was permitted by their 1959 decision with effect on the 1st of January 2023.
The nautical mile historically also called sea mile was originally defined as one minute of arc along a meridian of the Earth. Navigators use dividers to step off the distance between two points on the navigational chart. They then place the open dividers against the minutes-of-latitude scale at the edge of the chart. They read off the distance in nautical miles. The Earth is not perfectly spherical but an oblate spheroid. So the length of a minute of latitude increases by 1% from the equator to the poles. Since 1929 the international nautical mile is defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 meters. The data mile used in radar-related subjects is equal to 6,000 feet or 1.8288 kilometers. The radar mile is a unit of time equal to the time required for a radar pulse to travel a distance of two miles. Thus the radar statute mile is 10.8 microseconds and the radar nautical mile is 12.4 microseconds. Scandinavians used their own version of the nautical mile up to the beginning of the 20th century. It was indigenously known as a sea mile.
Common questions
What is the origin of the word mile?
The modern English word mile derives from Middle English and Old English, which was cognate with all other Germanic terms for miles. These derived from the nominal ellipsis form of 'mile' or 'miles', the Roman mile of one thousand paces.
When was the English statute mile established by law?
The English statute mile was established by a Weights and Measures Act of Parliament in 1593 during the reign of Queen Elizabeth I. The applicable passage of the statute reads: A Mile shall contain eight Furlongs, every Furlong forty Poles, and every Pole shall contain sixteen Foot and half.
How long is the international mile in meters?
The international mile is precisely equal to 1609.344 meters. It was established as part of the 1959 international yard and pound agreement reached by the United States, the United Kingdom, Canada, Australia, New Zealand, and the Union of South Africa.
Why did the US retire the survey mile on January 1st 2023?
In October 2019, US National Geodetic Survey and National Institute of Standards and Technology announced their joint intent to retire the US survey foot and US survey mile. This was permitted by their 1959 decision with effect on the 1st of January 2023.
What is the exact length of the international nautical mile defined since 1929?
Since 1929 the international nautical mile is defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 meters. The Earth is not perfectly spherical but an oblate spheroid so the length of a minute of latitude increases from the equator to the poles.