Definition of Nautical Mile

A nautical mile is a unit of distance, or length, as physical scientists like to call it. The derived unit of speed is the knot, defined as one nautical mile per hour. Both nautical miles and knots are widely used around the world for maritime and aviation purposes.

The nautical mile was historically defined as a minute of arc along a great circle of the Earth. It can therefore be measured on a meridian as change of latitude on a nautical chart. Slight variations in national definitions were settled in 1929, when the International Extraordinary Hydrographic Conference, Monaco adopted a definition of 1 nm = 1,852 metres. The United States adopted it in 1954. The Royal Hydrographic Office of the United Kingdom converted in 1970.