Difference Between Mile and Nautical Mile

Main Difference – Mile vs. Nautical Mile

Miles and nautical miles are both units used to measure distances and the main difference between the mile and the nautical mile is that the mile is 1.609344 km whereas the nautical mile is 1.852 km. A Nautical mile is a unit used to measure distances at the sea. 

What is a Mile

Mile is a unit used to measure distances on land. At present, in most parts of the world, the mile as an official unit to measure distance has largely been replaced by the kilometer (even though the mile is still widely used informally). Traditionally, there had been several different “miles” used for distance measurement around the world. Notably, the British mile had been based on the length of feet of kings. However, standard rods to define the foot developed later on in England, and the mile also became standardized as a consequence. In 1959, under the International Yard and Pound Agreement, a new international mile was agreed upon by several countries, with 1 international mile defined to be exactly equal to 1.609344 km.

An ancient Roman milestone

What is a Nautical Mile

A Nautical mile is a unit used to measure distances at the sea. Although the unit is not an official SI unit, it is still widely used by sea and air navigators. Traditionally, the nautical mile had been defined as the length of a minute of arc of a longitude (a line running through The Poles roughly in a circle). This corresponds to a length which is   of the length of the longitude. Using a distance unit based on a longitude has an advantage when working with flat maps which use projections and hence distort the actual shape of Earth. However, since the Earth is not a perfect sphere, the length of the nautical mile along the Earth’s surface is slightly smaller closer to the equator than at the poles. These two values differ by about 1%. In order to overcome this discrepancy, the nautical mile was redefined to be exactly equal to 1.852 km at the International Extraordinary Hydrographic Conference in 1929.

Difference Between Mile and Nautical Mile

Current Definition

An international mile is 1.609344 km.

A nautical mile is 1.852 km.

Traditional Definition

The mile was based on the length of a standard rod which was used to define the foot.

The nautical mile was defined to be the length of a minute of arc of a longitude.

Usage

The use of the mile is not restricted to any specific fields.

The nautical mile is used by air and sea navigators.

Image Courtesy

“Milestone XXIX from the Via Romana XVIII, which connected Bracara Augusta to Asturica Augusta. Roadside with milestone” by Júlio Reis (Own work) [CC BY-SA 3.0], via Wikimedia Commons