The geographical mile is an international unit of length determined by 1 minute of arc—1/60 degree—along the Earth's equator. For the international ellipsoid 1924 this equalled 1855.4 metres. The American Practical Navigator 2017 defines the geographical mile as 6,087.08 feet (1,855.342 m). Greater precision depends more on choice of ellipsoid than on more careful measurement: the length of the equator in the World Geodetic System WGS-84 is 40,075,016.6856 m, which makes the geographical mile 1,855.3248 m, while the IERS Conventions (2010) takes the equator to be 40,075,014.1723 m, making the geographical mile 1,855.3247 m, 0.1 millimetres shorter. In any ellipsoid, the length of a degree of longitude at the equator is thus exactly 60 geographical miles.

The shape of the Earth is a slightly flattened sphere, which results in the Earth's circumference being 0.168% larger when measured around the equator as compared to through the poles. The geographical mile is slightly larger than the nautical mile (which was historically linked to the circumference measured through both poles); one geographic mile is equivalent to approximately 1.00178 nautical miles.