The short answer: we inherited the 60-based (sexagesimal) counting system from the Babylonians, who used base 60 for mathematics and astronomy. The 24-hour day comes from ancient Egyptians, who divided daylight and darkness into 12 parts each. Together, these two ancient choices gave us the time units we use today: 24 hours in a day, 60 minutes in an hour, 60 seconds in a minute.
The Babylonian Base 60 System
Start with the Babylonians. They used a base-60 number system, inherited from the Sumerians. Unlike our base-10 system, which counts in tens, the Babylonian system counted in sixties. This was not random. It made mental arithmetic far easier for their astronomers and traders.
Why 60? Because 60 is divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. You can split an hour into halves, thirds, quarters, fifths, sixths, tenths, twelfths, and still get a whole number of minutes. In base-10, you can only divide evenly by 2 and 5. The Babylonians valued that flexibility, so they kept it.
Why 24 Hours in a Day
The other half of the story comes from the ancient Egyptians. They split daylight into 12 parts and night into another 12, giving 24 hours total. They used 12 because it is convenient for counting on finger knuckles and because it appears naturally in the lunar calendar.
Those early hours were not fixed. They were seasonal: the length of an hour changed through the year. In summer, daylight hours stretched longer than night hours. In winter, the reverse. That system worked for centuries, but it created problems for anyone who needed a consistent measure.
Equal Hours Arrive
Equal-length hours became standard only with mechanical clocks in the 14th century. Once clocks could tick at a steady rate, it made sense to divide the day into 24 equal parts. That is when the 24-hour day we use today really took hold. The seasonal hours did not disappear overnight, but the equal-hour system won out because it was simpler for trade, travel, and science.
Minutes and Seconds the Small Parts
Once you have hours, you need smaller units. The words 'minute' and 'second' come from Latin. 'Minute' comes from pars minuta prima, meaning 'first small part.' 'Second' comes from pars minuta secunda, meaning 'second small part.' An hour divides into 60 first small parts, and each of those divides into 60 second small parts.
Why 60 again? The Babylonians had already established base 60 for dividing the circle into 360 degrees and then into 60 arcminutes. The same system that worked for angles worked for time. The minute and second are direct descendants of the sexagesimal system.
Why Not 100?
You might wonder why we did not just use 100, like the metric system. The answer is historical momentum. By the time decimal time was attempted, the 60-based system was already embedded in astronomy, navigation, and daily life. Changing it would have required rewriting every table, every clock face, every calculation. The cost was too high, so we kept the old units.
Decimal Time in France
One serious attempt to switch to decimal time did happen. Revolutionary France brought in decimal time in 1793, with 10 hours of 100 minutes of 100 seconds. The new system was compulsory for a while. It did not last.
Compulsory use was suspended in 1795. People found it confusing because their clocks and watches still showed 12 or 24 hours. The new system also did not divide evenly into weeks or months, which caused friction. The experiment failed, and France went back to the 24-hour day and 60-minute hour.
The Same System in Angles
A circle has 360 degrees for the same reason an hour has 60 minutes: Babylonian astronomy. They divided a circle into 360 degrees, each degree into 60 arcminutes, each arcminute into 60 arcseconds. Exactly the same structure as hours, minutes, and seconds.
That is no coincidence. The Babylonians used the same sexagesimal system for both time and angles because it made trigonometric calculations easier. When you look at a clock, you are looking at a 360-degree circle divided into 12 hours, then each hour into 60 minutes, each minute into 60 seconds. The parallel is direct.
Next time you see 3:45:30, you are looking at a relic of ancient Sumerian mathematics. The system has survived thousands of years because it is practical, even if it is not decimal.
What a Day Actually Contains
Putting it all together: a day is 86,400 seconds long. That is 24 hours times 60 minutes times 60 seconds. The number comes directly from two ancient systems: the Egyptian 24-hour day and the Babylonian base-60 division of each hour.
- 24 hours per day (from Egypt)
- 60 minutes per hour (from Babylon)
- 60 seconds per minute (from Babylon)
That multiplication gives you 86,400 seconds. It is a large number, but also highly composite: it has many divisors. You can split a day into halves, thirds, fourths, sixths, eighths, tenths, twelfths, fifteenths, twentieths, thirtieths, and still get a whole number of seconds. A direct benefit of the base-60 choice.
Why it Matters Today
This is not just ancient history. The reason we keep 60 minutes in an hour is practical. When you are cooking, timing a workout, or calculating travel time, being able to divide an hour into thirds or quarters without fractions is genuinely useful. Twenty minutes is one-third of an hour. Fifteen minutes is one-quarter. Try doing that with a 100-minute hour.
That is why the system persists even though most of the world uses metric for length and weight. Time is the one place we still use base 60, and it works. Next time you use a stopwatch or set a timer, you are relying on a system thousands of years old. To see it in action, use the tools on aceclock.com to measure your own 60 minutes or 24 hours.