Historical definition – 1 nautical mile
Visual comparison of a kilometre, statute mile, and nautical mile
A nautical mile (also known as an air mile) is a unit of measurement defined as exactly 1,852 metres (6,076.12 ; 1.15078 mi).
Historically, it was defined as one minute of latitude, which is one sixtieth of a degree of latitude – i.e. the polar circumference of 40,075.017 km x 1/60 x 1/360 = 1,855.3 metres (6,087 ft); this is known as the geographical mile.
It is a non-SI unit which today has a continued use in both air and marine navigation, and for the definition of territorial waters.
One tenth of a nautical mile is a cable length. The derived unit of speed is the knot, defined as one nautical mile per hour.
There is no single internationally agreed symbol.
While using M itself, the International Bureau of Weights and Measures recognises that NM, Nm and nmi are also in use.