Why There Are 60 Minutes In An Hour

You count money in tens. You count distance in tens. You count almost everything in base-10, because humans have 10 fingers and that's how counting started. So why does an hour have 60 minutes and a minute 60 seconds? Why not 100?

The question

Where did 60 come from?

The reveal

It came from the Sumerians, around 2000 BCE, four thousand years ago, in what is now southern Iraq. Their counting system was base-60 — a sexagesimal system.

Why base-60?

The Sumerians didn't pick 60 by accident. It's a highly composite number — divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. You can split 60 into halves, thirds, quarters, fifths, sixths, tenths, and twelfths without ever producing a fractional remainder. Try that with 10: you can do halves and fifths cleanly, but thirds and quarters produce ugly fractions.

For trade, astronomy, and calendar work — the Sumerians' specialties — being able to divide cleanly is more useful than being able to count on fingers. They invented a system that's friendly to thirds and quarters, the fractions humans use most.

The Babylonians inherit it

Around 1800 BCE, the Babylonians absorb Sumerian astronomy and math. They keep base-60. They divide the circle into 360 degrees (because 6 × 60 = 360, and the year was thought to have ~360 days). Each degree was divided into 60 arcminutes, each arcminute into 60 arcseconds.

The Greeks inherit it

Around 150 BCE, the Greek astronomer Hipparchus divides the day into 24 hours. Ptolemy later divides each hour into 60 "minuta" (Latin for "first small division") and each minuta into 60 "secunda" (the "second small division"). This is where the words minute and second come from — they're literally "first subdivision" and "second subdivision" of an hour, in Latin.

The mechanical clocks

When mechanical clocks arrive in medieval Europe (~1300 CE), they need to divide time. The natural unit is the one astronomers have used for 3,000 years: 60. Clockmakers inherit the Babylonian-Sumerian choice. They could have used 100. They didn't, because astronomers had been using 60 for two millennia, and clocks were built to match the existing astronomical tables.

Why we still use it

We keep 60 because changing it is catastrophic. Every clock, calendar, angle measurement, scientific paper, navigation chart, GPS system, financial timing system, and piece of software on Earth is built around 60-minutes-per-hour. The cost of switching to a base-10 time system is, conservatively, in the trillions of dollars, plus the inconvenience of every human alive.

The French tried. In 1793, the new Revolutionary government introduced decimal time: 10-hour days, 100-minute hours, 100-second minutes. It was abandoned within two years. Nobody used it.

The lesson

Time is the oldest continuously used measurement system on Earth. The minute and the second have been continuously used, in essentially the same form, for over 2,000 years. The choice of 60 is older than the alphabet, older than most religions, older than the calendar year itself.

Every time you glance at a clock and see :60 at the edge of the minute, you're participating in a count invented by a civilization that died 4,000 years ago. They picked 60 because it divides cleanly. We've never had a good enough reason to switch.

A minute is 60 seconds because the Sumerians wanted easy thirds. Four thousand years later, we still owe them for it.