Why 24 hours in a day? Why not 10 or 100? – for 4T learning about time


For 4T's original post...


Hello 4T,

Time is an interesting topic. It seems so simple at first but why are there 24 hours in a day? Why not 200 hours or 10 hours? Why are there 60 minutes in an hour? Why not 100 minutes?

Schools and students have permission to use this graphic for non-commercial, educational purposes.

The time is 48 minutes past 7. That is 07:48.

What do I know about time?

I had often wondered why we had 24 hours in a day. From what I have been able to find out, one explanation comes from the Ancient Egyptians giving us the 24 hour day.

We count in what is called base 10 using the digits 0 to 9 (10 digits). The Ancient Egyptians counted in base 12. They divided the day into 12 hours of day and 12 hours of night.

Here is a link about the 24 hour day…



Another suggestion is the times came from the Ancient Babylonians. Unlike the Egyptians, they counted in base 60. 6, 12, 60 and 360 were important for them. They had 12 signs of the zodiac in the sky, divided the day into 12 hours of day and 12 hours of night, had 60 minutes in an hour and divided circles into 360 parts. Here is a link to the answer…



I think I prefer the Babylonian explanation better as it covers extra important numbers. Even though we now use base 10 numbers, we have kept the old divisions of the day for thousands of years.

With all of the above, where do we get a.m. and p.m.?

a.m. comes from the Latin “ante meridiem” meaning before midday

p.m. comes from the Latin “post meridiem” meaning after midday


In my diary, I like to use 24 hour time. 2:30 can be in the morning or afternoon unless we add a.m. or p.m.. 24 hour time makes it easier for me…

02:30 or 0230 – is 2:30 a.m.

14:30 or 1430 – is 2:30 p.m.


When is the best time of the day?

For me, the best time of day isn’t any set time. It’s when I’m doing something I enjoy whether commenting on blogs, writing stories, hiking in a national park, going to the cinema, listening to music as I work, making DVDs or speaking to friends.

What is my favourite time?

00:00 (that’s midnight) because I have usually logged off the computer for the night or 06:00 when I normally wake in the morning to see what has been happening in the world.

Keep blogging, everyone. I enjoyed your time post.


Teacher (retired), N.S.W., Australia


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I just had another thought to add to this post... If we did have 10 hours in a day, 5 for the day and 5 for the night, 100 minutes in an hour and 100 seconds in a minute what difference would we see in the amount of minutes and seconds in a day?

24 hours, 60 minutes, 60 seconds

24 hours = 24 x 60 minutes = 1,440 minutes = 1,440 x 60 seconds = 86,400 seconds in a day

1 day has 24 hours or 1,440 minutes or 86,400 seconds

10 hours, 100 minutes, 100 seconds

10 hours = 10 x 100 minutes = 1,000 minutes = 1,000 x 100 seconds = 100,000 seconds in a day

1 day has 10 hours or 1000 minutes or 100,000 seconds

This means there would be 440 less minutes in the 10 hour day but 13,600 seconds more. It's easier to work out the numbers for a 10 hour day. Our modern time might have been very different if the Babylonians and Egyptians had base 10 numbers like us.

Which do you think is better, the 24 hour or 10 hour day?


5 thoughts on “Why 24 hours in a day? Why not 10 or 100? – for 4T learning about time

  1. That Guy

    A problem with your question: “Which do you think is better, the 24 hour or 10 hour day?”, I don’t think that’s the right comparison. The Egyptians used the 12 base, not the 24 base, so they had 12 hours in the day, and 12 at night, which equals 24 hours in a day. Since we use 10 base, it would be 10 hours for day and 10 hours at night, so it would be a 20 hour day. So the question should read: “Which do you think is better, the 24 hour day or the 20 hour day.”.

    1. rossmannell

      Post author

      Thanks for the comment. You make a fair point. I was thinking of a clock showing 10 hours as compared to one showing 12 hours so that would be a 20 hour period if I were to divide the day into night and day. :)

    2. rossmannell

      Post author

      I have further reviewed what was written and your comment. I understand your suggestion for the 20 hour day using base 10 to divide the day into two units of 10 hours but, as I recall, my idea was the entire day be only a total of 10 hours.

      Dividing a day into 12 hours of night and 12 hours of day isn’t accurate in our method of telling time as our clocks start anew at midnight, thus our a.m. and p.m.. Both segments include night and day.

      If we were to review our use of time, my suggestion would give units of time more in line with base 10 without the need for a.m. or p.m. settings. We would know 5:00:000 meant midday whereas 00:00:000 would be midnight.

      On doing the calculations for 24 hour versus 10 hour day, I noted the number of hours would obviously drop by more than half and minutes by around 30% but seconds would increase around 16%. These figures are much closer in alignment than a 20 hour day with 100 minutes an hour and 100 seconds in a minute.

      The post was merely a suggestion of something as an alternative. As such, your 20 hour day with 10 hours of a.m. and 10 hours of p.m. is just as valid.

      Thanks for taking the time to comment and start me thinking again. :)

  2. Hobbs

    “It’s easier to work out the numbers for a 10 hour day.”

    But only because we use a base-10 system. I would prefer it if we used base 12. Divisibility FTW!


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