A nautical mile (symbol M, NM or nmi) is a unit of distance that is approximately one minute of arc measured along any meridian. By international agreement it has been set at 1,852 metres exactly (about 6,076 feet).

Speed at sea is measured in knots, a knot being one nautical mile per hour.

A mile on land (statute mile) is 1760 yards (1609.3m).

The standard nautical mile is taken as 6080 feet (1.151 statute miles or 1853m).

The nautical mile was historically defined as a minute of arc ( of a degree) along any of the Earths meridians (any of the north-south latitude lines), making a meridian exactly historical nautical miles.

The nautical mile can therefore be used to closely approximate a change of latitude (in degrees) on a nautical chart.

For example, traveling 120 Nm south along a meridian is equivalent to : change in latitude towards the south.