Nautical Miles to Miles

The nautical mile was born from navigation, not from farm fields. One minute of arc of latitude, a sixtieth of a degree, measured along a meridian is close to 1,852 m, so a navigator with a chart can measure distance directly against the latitude scale on its side: 60 nautical miles equal one degree of latitude. Because the Earth is slightly flattened, the true length of a minute varies from about 1,843 m at the equator to 1,862 m at the poles, which is why an agreed standard was needed.

The International Hydrographic Conference in Monaco set the international nautical mile at exactly 1,852 m in 1929. The United States adopted it in 1954, and the United Kingdom gave up its own Admiralty mile of 6,080 ft in 1970. In feet, the international nautical mile is about 6,076, compared with 5,280 for the statute mile.

A knot is one nautical mile per hour, so the same factor turns knots into miles per hour. A container ship sailing at 20 knots is doing 23 mph, and a jet cruising at 480 knots true airspeed covers about 552 statute miles an hour. Saying knots per hour is a common error, because the per hour is already in the unit.

Pilots file flight plans and receive wind reports in nautical miles and knots everywhere in the world, even in countries that use kilometers on the ground. Airline route maps sometimes show statute miles for passengers, so a 2,500 nmi transatlantic leg appears as about 2,877 mi.

Maritime law counts in nautical miles. Under the 1982 UN Convention on the Law of the Sea, territorial waters extend 12 nmi from the baseline, which is 13.81 statute miles, and an exclusive economic zone reaches 200 nmi, about 230.2 mi. News reports that quote these limits in plain miles sometimes forget to convert, so the numbers end up roughly 15% too small.

To go from statute miles to feet, use miles to feet; kilometers and other lengths are in the unit converter.