The nautical mile is the international unit of measure. 1[n mile] = 1852[m]. It is equal to the length of the arc of the Earth's elliptical meridian corresponding to one minute of latitude (one degree is equal to sixty minutes; a circumference is 360 degrees).

Because the Earth's meridian circle is an ellipse, its curvature is different at different latitudes, and therefore the arc length corresponding to one minute of latitude is not equal.

1 nautical mile = twice the length of the meridian ÷ 360 ÷ 60 ≈ 1852.25 - 9.31cos(2Ωm). In layman's terms, this means that the circumference of the earth where the earth's meridian is located is divided into 360 degrees, and each degree is further divided into 60 minutes, and the length of each minute is the average nautical mile length. δ is the latitude. When δ = 0 degrees, i.e., near the equator, the length of 1 nautical mile is the shortest, 1842.94 m; near the poles it is the longest (δ = 90 degrees), 1861.56 m. At about 44 degrees and 14 minutes, the length of a 1 n mile is equal to 1852 m. This is the length of 1 nautical mile that will be used by our country and most of the world by 2019, as adopted by the International Conference on Hydrography of 1929 ( International Extraordinary Hydrographic Conference) adopted as the standard length of the nautical mile.

1 nautical mile = 1.852 kilometers (km) (Chinese standard)

1 nautical mile = 1.85101 kilometers (km). (US standard)

1 nautical mile = 1.85455 kilometers (km). (British standard)

1 nautical mile = 1.85327 kilometers (km). (French standard)

1 nautical mile = 1.85578 kilometers (km). (Russian standard)

The shortest nautical mile is at the equator, where 1 nautical mile = 1,843 meters.

The longest nautical miles are on the North and South Poles, 1 nautical mile = 1862 meters.

The average radius of the Earth is 6371300m, and 1 nautical mile calculated from the average radius of the Earth is:

1 nautical mile = 2*π*6371300/360/60=1853.3m

The Chinese language used to represent the nautical mile with a two-syllable Chinese character, 浬(读音：lǐ或hǎilǐ), which has now been abolished, but is still used in Taiwan.

Knot

Knot used to be used by the crew to measure the speed of the ship. For every 1 nautical mile, the crew would put a knot on the rope they put down, and later on, knots would be used as the unit of ship's speed.

1 knot = 1 nautical mile/hour = (1852/3600) m/s is the unit of speed, 1 nautical mile = 1852m is the unit of length