Nautical mile

A nautical mile is a unit of measurement used in both air and marine navigation,[2] and for the definition of territorial waters.[3] Historically, it was defined as one minute (1/60) of a degree of latitude. Today it is defined as exactly 1852 metres. The derived unit of speed is the knot, one nautical mile per hour.

Nautical mile
Unit systemNon-SI unit
Unit ofLength
SymbolM, NM, or nmi 
1 M, NM, or nmi in ...... is equal to ...
   metre   1852[1]
   foot   ≈6076
   statute mile   ≈1.151
   cable   10
Nautic mile definition v2 English
Historical definition – 1 nautical mile
Visual comparison of a kilometre, statute mile, and nautical mile

Unit symbol

There is no single internationally agreed symbol.[1]

While using M itself, the International Bureau of Weights and Measures recognises that NM, Nm and nmi are also in use.[1]


The word mile is from the Latin word for a thousand paces: mille passus. Navigation at sea was done by eye[10] until around 1500 when navigational instruments were developed and cartographers began using a coordinate system with parallels of latitude and meridians of longitude.

In 1617 the Dutch scientist Willebrord Snell assessed the circumference of the Earth at 24,630 Roman miles (24,024 statute miles). Around that time British mathematician Edmund Gunter improved navigational tools including a new quadrant to determine latitude at sea. He reasoned that the lines of latitude could be used as the basis for a unit of measurement for distance and proposed the nautical mile as one minute or one-sixtieth (1/60) of one degree of latitude. As one degree is 1/360 of a circle, one minute of arc is 1/21600 of a circle (or, in radians, π/10800). These sexagesimal (base 60) units originated in Babylonian astronomy. Gunter used Snell's circumference to define a nautical mile as 6,080 feet, the length of one minute of arc at 48 degrees latitude. Since the earth is not a perfect sphere but is an oblate spheroid with slightly flattened poles, a minute of latitude is not constant, but about 1861 metres at the poles and 1843 metres at the Equator,[1] with a mean value of 1852.3 metres. France[11] and other countries measured the minute of arc at 45 degrees latitude, making the nautical mile 1852 metres.[10]

The Admiralty measured mile, or British nautical mile, 6,080 feet, was derived from the Admiralty knot, 6,080 imperial feet per hour. The U.S. nautical mile was 6,080.20 feet, based in the Mendenhall Order foot of 1893.

In 1929, the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 metres.[1] The United States did not adopt the international nautical mile until 1954.[12] Britain adopted it in 1970, and references to the obsolete unit are converted to 1853 metres.[13]

Similar definitions

The metre was originally defined as ​110000000 of the meridian arc from the North pole to the equator passing through Dunkirk. The Earth's circumference is therefore approximately 40,000 km. The equatorial circumference is slightly longer than the polar circumference – the measurement based on this (40,075.017 km × 1/60 × 1/360 = 1855.3 metres is known as the geographical mile.

See also


  1. ^ a b c d e f Göbel, E.; Mills, I.M.; Wallard, Andrew, eds. (2006). The International System of Units (SI) (PDF) (8th ed.). Paris: Bureau International des Poids et Mesures. p. 127. ISBN 92-822-2213-6. Retrieved 2017-06-20.
  2. ^ "mile | unit of measurement". Encyclopædia Britannica. Retrieved 2016-06-10.
  4. ^ Symboles, Abréviations et Termes utilisés sur les cartes marines [Symbols, Abbreviations and Terms used on Charts] (PDF) (in French and English). 1D (INT1) (6 ed.). Service Hydrographique et Océanographique de la Marine (SHOM). 2016. Retrieved 2018-01-04. also available as Symbols and Abbreviations used on ADMIRALTY Paper Charts. NP5011 (6th ed.). United Kingdom Hydrographic Office. 2016. section B, line 45. ISBN 978-0-70-774-1741.
  5. ^ "WS SIGMET Quick Reference Guide" (PDF). ICAO. ICAO. Retrieved 2016-06-09.
  6. ^ International Standards and Recommended Practices, Annex 5 to the Convention on International Civil Aviation, “Units of measurement to be Used in Air and Ground Operations”, ICAO, 4th Edition, July 1979.
  7. ^ "Law of the Sea". NOAA. Retrieved 2016-06-09.
  8. ^ "APPENDIX A: SYMBOLS AND PREFIXES". IEEE. Retrieved 2016-06-09.
  9. ^ "U.S. Government Printing Office Style Manual". U.S. Government Printing Office. Retrieved 2016-06-10.
  10. ^ a b "Mile, Nautical and Statute – FREE Mile, Nautical and Statute information | Find Mile, Nautical and Statute research". Retrieved 2016-06-10.
  11. ^ "MILLE MARIN : définition de MILLE MARIN et synonymes de MILLE MARIN (français)". Retrieved 2018-12-23.
  12. ^ Astin, A.V.; Karo, H. Arnold (June 25, 1959). "Refinement of values for the yard and the pound" (PDF). NOAA. National Bureau of Standards. Retrieved 2018-07-07.
  13. ^ "The Units of Measurement Regulations 1995". Retrieved 2016-06-10.
Bistra Glacier

Bistra Glacier (Bulgarian: ледник Бистра, ‘Lednik Bistra’ \'led-nik 'bis-tra\) is 1 nautical mile (1.9 km; 1.2 mi) long and 0.4 nautical miles (0.74 km; 0.46 mi) wide glacier on the northwest side of Imeon Range on Smith Island in the South Shetland Islands, Antarctica. It is situated southwest of Chuprene Glacier and northwest of Dragoman Glacier, drains the west slopes of Mount Foster and the north slopes of Slaveykov Peak, and flows northwestwards of Zavet Saddle to enter Drake Passage south of Garmen Point.

The glacier is named after the settlements of Bistra in northeastern Bulgaria.

Burketown Airport

Burketown Airport (IATA: BUC, ICAO: YBKT) is an airport located 1 nautical mile (1.9 km; 1.2 mi) southwest of Burketown, Queensland, Australia.

Earth's circumference

Earth's circumference is the distance around the Earth, either around the equator (40,075.017 km [ 24,901.461 mi ]) or around the poles (40,007.86 km [ 24,859.73 mi ]).

Measurement of Earth's circumference has been important to navigation since ancient times. It was first calculated by Eratosthenes, which he did by comparing altitudes of the mid-day sun at two places a known north–south distance apart. In the Middle Ages, Al Biruni calculated a more accurate version, becoming the first person to perform the calculation based on data from a single location.

In modern times, Earth's circumference has been used to define fundamental units of measurement of length: the nautical mile in the seventeenth century and the metre in the eighteenth. Earth's polar circumference is very near to 21,600 nautical miles because the nautical mile was intended to express 1/60TH of a degree of latitude (i.e. 60 × 360), which is 21,600 partitions of the polar circumference. The polar circumference is even closer to 40,000 kilometres because the metre was originally defined to be one 10-millionth the distance from pole to equator. The physical length of each unit of measure has remained close to what it was determined to be at the time, but the precision of measuring the circumference has improved since then.

Treated as a sphere, determining Earth's circumference would be its single most important measurement (Earth actually deviates from a sphere by about 0.3% as characterized by flattening).

Fort Deposit–Lowndes County Airport

Fort Deposit–Lowndes County Airport (FAA LID: 67A) is a city-owned public-use airport located one nautical mile (2 km) southwest of Fort Deposit, a town in Lowndes County, Alabama, United States.

Growler Rock

Growler Rock (62°7′S 58°8′W) is a rock 1 nautical mile (2 km) northwest of Lions Rump in the western part of King George Bay, King George Island, in the South Shetland Islands. It was charted and named during 1937 by Discovery Investigations personnel on the Discovery II. The term "growler" is used to denote small pieces of ice barely showing above water.

Hauken Rock

Hauken Rock (62°1′S 57°33′W) is a rock lying nearly 1 nautical mile (2 km) east of the Ornen Rocks and 2 nautical miles (4 km) northeast of Cape Melville, the eastern extremity of King George Island, in the South Shetland Islands. It was named by the UK Antarctic Place-Names Committee in 1960 from association with Ornen Rocks. Hauken and Ørnen, the first two modern whale catchers, accompanied the floating factory ship Admiralen to the South Shetland Islands in January–February 1906.

Jaluit Airport

Jaluit Airport is a public use airstrip located one nautical mile (1.85 km) southeast of the village of Jabor on Jaluit Atoll, Marshall Islands. This airstrip is assigned the location identifier N55 by the FAA and UIT by the IATA.

Knot (unit)

The knot () is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h (approximately 1.15078 mph). The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); kt is also common, especially in aviation where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.

Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.

Kowanyama Airport

Kowanyama Airport (IATA: KWM, ICAO: YKOW) is an airport located 1 nautical mile (1.9 km; 1.2 mi) southeast of Kowanyama, Queensland, Australia. In 2005 the airport received $107,448 for security upgrades.

McMinn Airport

McMinn Airport (FAA LID: 25A) is a privately owned public-use airport located one nautical mile (1.85 km) southwest of the central business district of Weaver, a city in Calhoun County, Alabama, United States.


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, Myanmar, 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.

Pine Hill Municipal Airport

Pine Hill Municipal Airport (FAA LID: 71A) is a town-owned public-use airport located one nautical mile (2 km) south of the central business district of Pine Hill, a town in Wilcox County, Alabama, United States.

Pittsburgh–Monroeville Airport

Pittsburgh–Monroeville Airport (FAA LID: 4G0) is a public-use airport located one nautical mile (1.8 km) north of the central business district of Monroeville, in Allegheny County, Pennsylvania, United States. The airport is privately owned by the estate of Helen M. Brown and is also known as the Harold W. Brown Memorial Field.The airport no longer offers aviation fuel for sale, but 2,000 planes land and take off at the airport every year, according to Weible. Pilots pay $3 on the honor system to defray the expenses of mowing the grass and maintaining the runway for an overnight stay.

The airport also hosts a gathering every other year for the Aero Club of Pittsburgh. The airport buildings also serve as the meeting place for Cadet Squad 604 of the Civil Air Patrol.

The airfield was used as a filming location in a pivotal scene in the 1978 horror film Dawn of the Dead.

Razboyna Glacier

Razboyna Glacier (Bulgarian: ледник Разбойна, ‘Lednik Razboyna’ \'led-nik raz-'boy-na\) is the 3 nautical miles (5.6 km; 3.5 mi) long and 1 nautical mile (1.9 km; 1.2 mi) wide glacier in Petvar Heights on the southeast side of Sentinel Range in Ellsworth Mountains, Antarctica situated north of Drama Glacier, east of Kornicker Glacier, and south of the lower course of Thomas Glacier. It is draining the north slopes of Bagra Peak, and flowing northeastwards to leave the range north of Long Peak.

The feature is named after the settlements of Razboyna in northeastern and southeastern Bulgaria.

St George Airport (Queensland)

St George Airport (IATA: SGO, ICAO: YSGE) is an airport 1 nautical mile (1.9 km; 1.2 mi) southeast of St George, Queensland, Australia.

Svalbard Treaty

The Svalbard Treaty (originally the Spitsbergen Treaty) recognises the sovereignty of Norway over the Arctic archipelago of Svalbard, at the time called Spitsbergen. The exercise of sovereignty is, however, subject to certain stipulations, and not all Norwegian law applies. The treaty regulates the demilitarisation of the archipelago. The signatories were given equal rights to engage in commercial activities (mainly coal mining) on the islands. As of 2012, Norway and Russia are making use of this right.

Uniquely, the archipelago is an entirely visa-free zone under the terms of the Svalbard Treaty.The treaty was signed on 9 February 1920 and submitted for registration in the League of Nations Treaty Series on 21 October 1920. There were 14 original High Contracting Parties: Denmark, France, Italy, Japan, the Netherlands, Norway, Sweden, the United Kingdom (including the dominions of Australia, Canada, New Zealand and South Africa, as well as India), and the United States. Of the original signatories, Japan was the last to ratify the treaty on 2 April 1925, and it came into force on 14 August 1925.Several additional nations acceded to the treaty after it was ratified by the original signatories. As of 2018, there are 46 parties to the treaty.

Tavares Seaplane Base

Tavares Seaplane Base (FAA LID: FA1) is a city-owned, public-use seaplane base located one nautical mile (1.85 km) southeast of the central business district of Tavares, a city in Lake County, Florida, United States.

Turbot War

The Turbot War (known in Spain as Guerra del Fletán) was an international fishing dispute between Canada (supported by the United Kingdom and Ireland) and Spain (supported by the European Union and Iceland) in which Canada stopped a Spanish fishing trawler from Galicia in international waters and arrested its crew. Canada claimed that European Union factory ships were illegally overfishing Greenland halibut, also known as Greenland turbot, on the Grand Banks, just outside Canada's declared 200-nautical-mile (370 km) exclusive economic zone (EEZ).

Umatilla Municipal Airport

Umatilla Municipal Airport (FAA LID: X23) is a public-use airport located 1 nautical mile (1.85 km) east of the central business district of the city of Umatilla in Lake County, Florida, United States. The airport is publicly owned.

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