Why Are There 60 Minutes in an Hour and 60 Seconds in a Minute?

We count almost everything in tens — fingers, decimals, percentages. Yet the clock stubbornly counts in sixties. That's not an accident of clockmaking; it's a 4,000-year-old inheritance from Mesopotamia.

The Babylonian base-60 legacy

Sumerian and Babylonian mathematicians worked in a sexagesimal (base-60) number system. Sixty is a remarkably practical base: it divides evenly by 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30, so halves, thirds, quarters and fifths all come out whole — a huge advantage when arithmetic was done by hand. Babylonian astronomers used it for their meticulous records of the heavens, dividing circles into 360 degrees.

Greek astronomers pass it on

Greek astronomers — Hipparchus, and later Ptolemy in the 2nd century AD — adopted the Babylonian convention, subdividing each degree into 60 partes minutae primae ("first small parts") and each of those into 60 partes minutae secundae ("second small parts"). Those Latin phrases are literally where the words minute and second come from. The same subdivision was applied to the hour, at first only on paper — no ancient device could measure a second.

And why 24 hours?

The Egyptians divided daylight into 12 (a count inherited from tracking star groups called decans, and handy for their base-12 finger-counting on knuckles) and night into 12 more — giving 24. Only with 14th-century mechanical clocks did hours become equal in length year-round, and only with pendulum clocks in the 1600s did the second become something a machine could actually tick.

So a modern watch face is a stack of ancient decisions: Egyptian hours, Babylonian sixties, Greek subdivisions, Latin names. Convert between all of them — seconds, minutes, milliseconds — or explore more units in Units of Time.