Nautical Mile


Definition of Nautical Mile

A nautical mile is a unit of measurement used by sailors, pilots, and navigators to measure distances over water and air accurately. The nautical mile was officially set at exactly 1.852 kilometers, or 1.1508 miles, in 1929 by the International Hydrographic Organization.

Nautical miles are essential for navigating on water and in the air, where land-measured miles or kilometers may not be precise.

Just like nautical charts, they’re based on the Earth’s latitude and longitude coordinates; one nautical mile is equal to one minute of latitude.

Nautical miles are also used to set the safety requirements for navigation lights. The navigation lights of a vessel must be visible from a predetermined distance in nautical miles, with the range increasing for bigger vessels.

The table below compares the varying ranges of navigation lights in nautical miles.

Navigation Light Nautical Miles
Masthead light 2–3
Sidelights 1–2
Stern light 2
Towing light 3
All-around light 3–5
Flashing light 5

Yet another application of nautical miles is calculating speed in knots. One knot is equivalent to one nautical mile per hour.

Fun Fact: Before the establishment of nautical miles, sailors measured speed using a weighted, knotted rope that the ship would drag through the water for a fixed period of time.

ship drags a knotted rope to measure the speed

Example of Nautical Mile in a Sentence

"Many fisheries are unregulated in international waters beyond 200 nautical mile exclusive economic zones of coastal countries,"

Synonyms: sea mile

Related Terms for Nautical Mile