24-Hour Clock

The all-time most popular post on this blog, with more than 146,000 views and 99 comments, is “European Date Format” (that is, rendering a date as date/month/year rather than the traditional U.S. month/date/year).

A communication I recently received from Amazon, giving instructions on returning an item to one of its Lockers, made me wonder if I might repeat that post’s success. Here’s what Amazon sent me:


The key is that “21:00.” The traditional American rendition of that time is 9:00 PM. So, I wondered, is there a trend of U.S. adoption of European time format?

For the purposes of this blog, the first question to answer is whether the 24-hour format is indeed a British thing. The answer is a bit mixed. I just read an entertaining free e-book on the subject called Counting Time: A Brief History of the 24-Hour Clock, by Peter Boardman. He recounts how this idea was broached following World War I, was adopted by the British Army and Navy, and was endlessly debated in the House of Lords and the letters pages of The Times in the 1920s and early ’30s. The Lords endorsed the 24-hour clock in 1933 and the BBC experimented with it the following year, but no one seemed to like the idea and it was pretty much dropped till 1964, when the railways and London Transport adopted. Boardman concludes, “Instead of having just one time system, we have two, and they’re both going to be with us indefinitely. ”

The book was published in 2011 and things may have changed in the intervening years, at least according to the responses I got when I asked British people on Twitter if they thought the 24-hour clock was common in the UK. Lynne Murphy said, “Very widespread–and I love it.” Mark Stradling ventured, “Written down, pretty much ubiquitous,” but noted a caveat: “Nobody talks like that, makes you sound like a robot.”

In the United States, the only home of 24-hour time has until now been the military, as one knows from movies where people talk about “Fourteen hundred hours.” But it’s also (not surprisingly) widespread in the computer world, which is presumably where Amazon picked it up.

In sum, I deem the 24-hour clock a Britishism and, in these parts, On the Radar. Let the page views and comments begin.


39 thoughts on “24-Hour Clock

  1. Hi Ben,

    An interesting tangent to the subject of the 24 Hour Clock which has always intrigued me is that “Military Time” (ie. the US adaptation of the 24hr clock) always seems to be rendered with a colon between the hours and minutes. Meanwhile a traditional British (transport timetable – e.g. https://www.eastmidlandstrains.co.uk/Documents/Menus/1/Timetable%20DEC%202017/TT1_web_PDF_Dec17.pdf) implementation would be four digits without punctuation.

    I am particularly conscious of this having been “picked up” on it in the past for having had the temerity to include a colon in my own usage of the 24hr clock.

    1. Every London train station I’ve been through definitely uses colons on its clocks and station departure boards (in 24hr of course). National Rail and TfL websites do as well when you’re looking up train times. I would assume the reason the EMT timetable doesn’t is simply space saving when the time is crammed into small table cells.

      If Americans don’t use 24hr at all, do station clocks and departure boards include an am/pm indicator, or is it just assumed you know what time of day it is?

  2. I remember traveling through continental Europe as a child with my parents and seeing clocks in stations with numbers 1 to 12 and around the outside, numbers 13 to 24. The original 24 hour clock!
    I’ve never seen this format in the U.K.

  3. As a 50-something Englander, my experience that the AM/PM distinction was colloquial, but 24-hour format was “official” (i.e taught at school).

    Similar to metric – people are conversant in varying degrees 🙂

  4. I’ve been using the 24 hour clock since at least when digital watches became a thing back in the seventies. This may have been because of my work with computers. Back then, you often had to re-enter the time every time you rebooted. I worked with one guy who never could get the hang of the 24 hour clock. You’d come in in the morning and the computer clock would read 21:00 because he’d rebooted it the evening before and entered the time as 4:00.

    Back in the eighties I was on holiday in the US and talking to a group of Americans. One wanted to know the time and I showed him my watch. It said 15:30 (or thereabouts). “Why is your watch on the 24 hour clock?” he asked. “Are you a doctor? Only hospitals use the 24 hour clock. And the military. You’re not in the military, are you?”

    Mind you, I heard a story some years ago from a British woman who was travelling to the US with a friend. They had to change planes in the US and their boarding passes gave the departure time as 16:30. By the time they got through immigration it was past four o’clock and they hurried to the gate, getting there at twenty past.

    “Why the hurry?” asked the check-in person. “Your flight doesn’t leave for two hours.”

    “It said 16:30 on the boarding pass.”

    “16:30 on the 24 hour clock is half past six.”

  5. Being a British coder since a very young age, I can’t recall a time when I personally didn’t understand the 24-hour clock. They do get used on timetables (rail, air) without the need for further explanation.

    Just one point about the colon, we do tend to have two forms, which is “four digits” where BOTH the hour and the minute are front-zero-padded and without a colon, starting at 0000 and up to 2359, and with a colon where only the minute is padded from 0:00 to 23:59.

    Most computer coders tend to use “epoch seconds”, which is the number of seconds since 1st January 1970 which can be represented using very simple maths (60 seconds = 1 minute, 3600 seconds = 1 hour etc). However, Microsoft Excel uses “date fractions” with 0 being 1st January 1900. To add a week, just add 7. Twelve hours, a half.

    There are various International Standards Organisations (ISO) date forms that tend to get used too, of which one popular one looks like this:

    2018-03-18 06:15:30

    Which is year-month-day hours:minutes:seconds – again using the 24-hour clock.

    However, it is interesting that if you look online at the TV schedule for the BBC television services, they are 24-hour


    But… they won’t be presented that way on-screen! “The BBC News at Six” is at 18:00 and the “BBC News at Ten” at 22:00.

    For some reason TV programmes tend to use the 12-hour clock, in the same way that a British weight-loss shows use stones (14 lbs, where 2.2lbs=1kg) but I never use anything other than kilograms in real life. Cookery shows use metric as does the Weather.

    So, your TV’s programme guide might use am/pm


    Or it might be 24-hour

  6. I would further add that the 24 hr clock is not just a Britishism, but a Europeanism. It’s correct that here in the UK it is only really used in writing (e.g. train timetables). No one would ever say “I’ll see you when I get home at 18 o’clock”, however one might say “I’ll be on the 15.35 train from Bristol,” quoting verbatim from the train timetable. Some European countries go a step further though: I have experience of Italy, where people do in fact generally speak in the 24 hour clock e.g. “ti vedo alle ore 15”, literally “I’ll see you at the hour of 15”.

    1. In Mark Steel’s Vive La Revolution, a stand-up history of the French Revolution, he recounts visiting the town of Sainte-Menehould, site of the staging post at which the king was recognised on his flight from Paris. (Allegedly, the local postman recognised him from his face on the coins.)

      Steel asked the manager of the local railway station when the next train was and was told half past five. Come six o’clock, no sign of the train. “I asked if he was sure about this train and he said with a gruffness worth of a million Gitanes, ‘Oui – cinq heures et demi – demain matin.'”

      I presume if he’d meant half past five that evening, it would have been dix-sept heures et demi.

  7. Incidentally, on the matter of shop opening times, I happened to be walking through Guildford town centre just now and I checked shop opening times wherever they were displayed. In the town centre, I think every shop had the times in am/pm. Some even dropped the am/pm and assumed you’d know the shop wouldn’t be opening from nine at night to five in the morning.

    There are some shops on the road back from the town centre to my house. Three of these did use the 24 hour clock. One was a chemists (i.e. pharmacy), one specialised in computer printers and the third was a Chinese travel agent.

    I suspect the 24 hour clock is more a continental Europe thing than a British thing.

  8. Calling this a “European time format” is a bit generous. 24-hour time is widely used in computing and IT everywhere, including the US. It’s often the default when printing a time, unless you explicitly specify a different format. Most IT workers are well accustomed to 24-hour time, as well as the ISO date format year-month-day. Given that Amazon is a tech company, I’m not surprised to see a 24-hour time in their communications, and it may have been a simple software oversight rather than any kind of stylistic choice; a programmer somewhere may have just failed to specify 12-hour time and left the default 24-hour time format.

    1. Why is it confusing? Just imagine one second past, and it makes total sense: post-meridian (after the middle on the day, noon) is the hour that starts with noon…

      1. Well, that’s one way of looking at it, but I’m too mathematical to see it that way. To me, noon is like zero, which is neither positive nor negative, so noon cannot be either before or after noon.

      2. And in mathematics we don’t write -0 either. We use the convention of writing zero without a minus sign, even though it is neither positive or negative.

      3. True, but I don’t think relevant. 12:00pm is like writing +0 – a unary plus sign not an addition operator.

        Actually, to me, 12:00pm obviously means midnight at the end of the day and 12:00am is midnight at the start of the day. Much better to use the 24 hour clock and avoid all this confusion.

    2. We had a meeting at work about “The Hitchhiker’s Guide to the Galaxy” a few weeks ago. The organiser had put a notice up advertising it as “12 PM”. That led to a discussion of what was meant by 12 PM.. As meridiem was noon, 12 post meridiem must be 12 hours after noon, and 12 ante meridiem must be 12 hours before noon. Therefore, 12 AM was the previous midnight and 12 PM was the following midnight.

      N.B. This wasn’t serious! It was just a bunch of IT people being “logical”!

  9. I wonder when 24 hour time was adopted in Europe and the UK specifically. Big Ben has 12 hour marks

    1. The kitchen clock I bought in Guildford town centre a couple of months ago has 12 hour marks. I don’t think I’ve ever seen on sale in the UK a dial clock with 24 hour marks.

      Incidentally, of course Big Ben is the bell, not the clock, and the whole thing is the Elizabeth Tower. I got varifocals last year (another Britishism, apparently). Before that, my long sightedness was so bad I needed to put my reading glasses on to read my watch. A couple of years ago I was walking through Westminster and I wanted to know the time. I didn’t want to fiddle to get my glasses out and I was wondering if there was a public clock near by. It had not occurred to e that I was walking across the road from the Houses of Parliament, and therefore the Elizabeth Tower.

    2. I remember bus time tables changing to 24 hour in the late 60s. The 12 hour clock is still used for most things. For example, my diving club pool sessions are at 8:30pm, not 20:30.

  10. Wars have almost been fought over the right to call a programme ‘News at 10’. If you said here is the ‘News at 22’ people would think you were nuts.

  11. I always read 24-hour clocks as 12-hour. My alarm clock for example, might say 20:30 but I automatically translate it to 8.30 pm. I didn’t realise 24-hour clocks were a British thing…

    1. Conversely, I sometimes accidentally hit the button on my watch that switches it from 24 hours to am/pm and then I look at the time and see 6:30 and wonder why I’m up at that unearthly hour of the morning.

  12. “I didn’t realise 24-hour clocks were a British thing…”
    They aren’t, in ordinary daily life.

    1. Reminds me that a few years ago I was walking through Guildford, actually heading to the station for a weekend away but still out of sight of the station, when someone stopped me and asked, “13:05 is five past one, right?” I said it was and he walked on (away from the station) without word of explanation

      1. 🙂

        Some years ago when my sister had moved into a new house, I was meeting up with my father and brother at my father’s house before we went to see her. My father revealed he’d bought a candle as a housewarming present. My brother then revealed he’d bought her a candle, too. I was immediately told to go out and buy two more candles.

  13. I don’t think this is a Britishism. As noted, the 24-hour clock is common in the US military. It also seems to be common in mass transit. I just looked at a few receipts for various things that I had around my place. The bus payment receipts issued for the “SBS” buses in New York use 24-hour notation. Likewise the receipts for MetroCard purchases issued by machines in the subway stations. The Metro North, LIRR, and NJ Transit regional rail systems all use 24-hour format on their receipts as well.

    As in the UK, this is a written standard only. People don’t speak that way.

  14. I first incountered the day/month/year
    format in the U.S. Navy in 1968. I was a
    Corpsman and while my memory is suspect
    I believe that was the format used in all military medical documents.

  15. As noted, 24-hour clocks are not a British thing and I find it a bit Anglocentric to confine this debate to an UK vs. US quirk. As can be read on Wikipedia, Italy adopted the 24-hour format at the end of the 19th century and was followed by other European countries (France, Belgium, etc.) long before the United Kingdom.
    In my experience, in France, the 24-hour format is commonly used, even in colloquial, everyday speech. 8 p. m. can be rendered as either ‘8 heures du soir’ or ’20 heures’.
    In Spain I think it is similar to the UK: all written communications are in the official format, but people commonly say “son las 7 de la tarde”‘ rather than “son las 19 (horas)”. A.m. and p.m. are virtually unknown in both France and Spain.


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