A slightly different topic to my usual claptrap this time…

Ever look at a digital clock that says “21:00” and convert it in your head to “9 o’clock”?

Most of us convert between 24 and 12 hour clocks easily without even thinking; we flip 21 to 9 or 15 to 3 without even really knowing we’re doing it (or at least I do anyway).

In Ireland and the U.K., we started using the 24-hour clock in our everyday lives around the 1960s and ’70s, despite various failed attempts at introducing it in the first half of the 20th century (mostly in the U.K.). It was first introduced by the military just during the First World War, and our first real exposure to it was with railway timetables in the ’60s. It is now used quite widely in everything from TV schedules to the default time format on our phones.

However… If you were to ask anyone for the time in Iruk (that’s my new name for Ireland and the U.K.), you would probably be told it in 12-hour format. Most TV/radio schedules, shop opening hours, advertisements etc are in AM/PM, although we do use a hodgepodge of both. Even within the same shop, website or TV station, you’ll often see a mix of both.

So, is one better than the other? As always, there’s pros and cons to everything!

Pros of 12-hour time

  • Distinct separation between morning and afternoon. This is not necessary, but it’s not a bad idea to divide the day into two distinct portions. Apparently there also exists a 6-hour clock, which divides the day into four. Here’s some more information if you’re bored.
  • Despite 24-hour being used quite a bit, most people speak in 12-hour. It’s been used for a long time and it’s pretty much engrained in how we think and speak the time.
  • Sounds better. For example, “5pm” sounds better than “17 hours”, but maybe that’s because it’s what I’m used to hearing.
  • Multiple ways of saying the same thing. For example at 6:00 pm you can say “six o’clock”, “6pm” or “six in the afternoon”. Also, words like “midnight”, “noon” and “midday” can be used. As they say, variety is the spice of life!

Cons of 12-hour time

  • Ambiguity. It’s easier to mistake times if you misread the AM/PM bit. We can’t be having you turn up for a train 12 hours too early, hence the train companies use the less ambiguous 24-hour clock, and have done since the ’60s. They could of course just use a different background colour for the morning and afternoon times, but 24-hour is preferred.

Pros of 24-hour time

  • Less ambiguous. For example, 6 o’clock doesn’t happen twice in one day.
  • Simpler. No “o’clocks”, “midnights” or “middays”, just simple hours and minutes. Also, the day is not divided into two – just one full 24 hour day.

Cons of 24-hour time

  • Pretty much all the pros for 12-hour can be counted as cons for 24-hour!

Some history…

There also exists a decimal time format that divides the day into 10 hours of 100 minutes. It was attempted during the French Revolution and again towards the end of the 19th century but failed on both occasions.

Diving the day into 24 hours come from ancient Egyptian times. They used a duodecimal numbering system and when they invented the sundial, it was divided into 12 hours. Night time was also divided into 12 hours for consistency, making 24 in total. 

We have the Babylonians to thank for there being 60 minutes in an hour. They used base-60 measurement systems as 60 is highly divisible (can be divided by 2, 3, 4, 5, 6, 10, 12 etc) and are responsible for dividing the hour into 60 minutes and minutes into 60 ‘second’ minutes.

Both 24 and 60 are quite useful, highly divisible numbers and despite it going back a long time, the foundations laid by the Egyptians and Babylonians have stuck over time. It’s quite interesting that the way we measure time has its origins from thousands of years ago. 

In summary…

I work in IT, and I wouldn’t expect to see time represented in any way other than 24-hour in a database or log file for example. But for whatever reason, good or bad, the 12-hour clock is still the most common format, at least when spoken. Despite my phone and other devices defaulting to 24-hour, I have now officially switched them to 12-hour because I always converted 24-hour back to 12 in my head anyway, and I figured why bother? It’s easy to do by the way, it’ll be under the date & time settings on your device if you want to be a rebel like me!

What do you prefer to use? Have your say in the discussion section below or on social media.

All the Time in the World
  • Adrian Liddle

    I don’t mind the 24 hour clock although I prefer am & pm but what does rile me is seeing either 12am or 12pm. It should either be 12hr or 2400hrs, or 12 noon or 12 midnight, after all what does 12 before noon or even 12 after noon mean which is what is being said by putting the am or pm after the 12!

    • I’ve never found the 12am/midnight thing confusing, but I can see how it makes more sense to start am/pm at 1 instead of 12. It’s just one of those things.