The nautical mile is used in navigation both at sea and in the air, due to its relationship with geographical coordinates.
The nautical mile was originally defined as one minute of arc along any meridian of earth, and in informal contexts is still defined in this way today. However, due to the fact that the earth is not a perfect sphere, the nautical mile defined in this way varies between approximately 1842 metres at the equator and 1861 metres at the pole.
In 1929 at the International Extraordinary Hydrographic Conference the nautical mile was defined as exactly 1852 metres.
The British nautical mile as used by the Admiralty originally related to distance on the surface of the earth just south of Great Britain, and was defined as being exactly 800 feet longer than a statute mile, making it exactly 6080 feet. The United Kingdom switched to the international definition of 1852 metres in 1970.
1 nautical mile is identical to
1 nautical mile is approximately equal to