Why Is a Circle 360 Degrees?

Wow and Flutter/CC-BY-2.0

It was the Babylonians who first divided the circle into 360 degrees in order to integrate the geometry they developed with the 360-day calendar then in use. The Babylonians devised a counting system based not on units of 10 but on units of 60, which can be counted to on the 12 knuckles of one hand and the five fingers of the other.

The sexegesimal counting system devised by the ancient Babylonians has left numerous marks on modern systems of geometry and mathematics. The number 60 is extremely convenient for rapid calculations, as it is a highly composite number that is divisible by all integers from 1 to 6, as well as 10, 12, 15, 20, 30 and 60. The Babylonians used a 360-day solar calendar, a 60-second minute and a 60-minute hour, according to The Story of Mathematics.

The Babylonians assigned 360 degrees to circles as an aid to time tracking. Using a 360-day calendar made it easy to associate each day of the year with an otherwise arbitrary partition of the circle, creating a convenient visual representation. Given the highly divisible nature of 60 and its multiples, the practice of dividing circles into 360 equal degrees has persisted ever since.