A circle of latitude on the Earth is an imaginary east-west circle connecting all locations (ignoring elevation) with a given latitude. A location's position along a circle of latitude is given by its longitude.

Circles of latitude are often called parallels because they are parallel to each other – that is, any two circles are always the same distance apart. Unlike circles of longitude, which all are great circles with the centre of Earth in the middle, the circles of latitude get smaller as the distance from the Equator increases. Their length can be calculated by a common sine or cosine function. The 60th circle of latitude is half as long as the equator (disregarding Earth’s minor ovality, which is less than 0.3%). A circle of latitude is perpendicular to all meridians.