I strongly advocate everyone learning using the 24 Hour clock verses our normal 12 hour clock.

I was in the military for 6 years and I am quite comfortable with it. My father was a pilot and he taught me the the 24 clock as well as the Phonetic Alphabet (which I also advocate), so I was familiar enough with it prior to entering into the military. It is simple enough to learn with a little diligent practice.

Problems With the 12 Hour Clock

The current problems we have with our 12 hour clock is that you always have to ask or wonder is this person meaning AM or PM, morning or afternoon, if they speak or write the time lazily or you catch the conversation out or context. Unless they specifically say AM or PM, or morning or afternoon or the contxt is quite clear, then this thought or annoying ponderance is there in the back of your mind. If I say 7 o’clock you need to know AM or PM in order to know what time a person is referring to, whereas if they say 19:00 you know it is at night.

There only a few countries left that use the 12 hour clock: the United States, Canada, and a few others.

Why Use the 24 Hour Clock

The 24 hour clock, conversely, is clear by the spoken or written numbers: 17:31 is 5:31pm or 03:35 is 3:35am. There is no potential alpha or numeric ambiguity possible with the time. It is easy to read and for your mind to parse instead of parsing both alpha and numeric characters, there are just a single set of numbers for your mind to interpret.

Much of Europe has moved to the 24 clock. Airlines, military, trains and other similar emergency and international and public services use the 24 hour clock for its simplicity, ease of use, and lack of ambiguity.

Learning the 24 Hour Clock

Learning the 24 Hour Clock is not so hard. Times from 1:00am to 12:00pm (noon) are written basically the same. It is written as follows: 2:30am = 02:30 (or 0230); 4:15pm = 16:15 (or 1615). See, it is not really that different.

After noon time things get a little trickier though. The hours after noon increase incrementally by 1 numerical hour from 1:00pm up until 12:00am (midnight), so you have 1:00pm is 13:00, 2:00pm is 14;00, and 3:00pm is 15:00… all the way up to 11:59pm which is 23:59. See! =)

Midnight Conventions

There are some conventions for telling the midnight hour. They are not really important since they all point to the same time. Use either and you will be understood.

If you are talking about the ending of a day or time period on midnight, it would be 24:00 since it would continue the day’s counting process. If you start a day at midnight they it would be 00:00 which shows a new day starting and not a continuance from the previous day’s activities or period.

That is about it. Both refer to the same time, so either way there will be no real confusion. Some use one and not the other.

Speaking 24 Hour Time

24 hour time is spoken as such: 02:00 would be said ‘oh two hundred hours’; 02:30 would be said ‘oh two hundred thirty hours’ or just ‘twenty two thirty’.

Telling 24 Hour Time On-The-Fly

This method is a little more difficult (in my humble opinion), but it will suffice until your get more familiar with it and then the following potentially simpler method may serve you better:

For hours greater than 12:00 you just subtract 2:00 from the time, and since the hour is automatically going to be a twelve or less you drop the first digit. Such as the following: 21:00 – you forget about the 20:00 portion of the time and just subtract the 02:00 from the hour leaving you 9:00 pm.

For times of 22:00 or greater you will remember they are a derivitive of 10:00 so you just add the 10:00 to the 0:00 and you have your time:

• 22:04 = 2:04 – 2:00 = 0:04 + 10:00 = 10:04pm
• 18:16 = 8:16 – 2:00 = 6:16pm
• 23:45 = 3:45 – 2:00 = 1:45 + 10:00 = 11:45pm
• 15:33 = 5:33 – 2:00 = 3:33pm

If you have any questions or comments feel free to add them here. If you have any resources or methods that simplify this process I would also like to hear it.  Below are some other resources that may assist you in learning the 24 hour clock including some study tools and a flash application or two.

References

Here are some references to help you to learn more about the 24 Clock as well as learn how to start telling time using the 24 hour clock. If you have found better resources please let me know.

• 24 Hour Clock (Absolute Astronomy)
• Military (Universal) Time Conversion
• Learn to Easily Interpret Military Time (Raam Dev’s Blog)
• 24 Hour Clock (Wikipedia)
• Time AM/PM vs the 24 Hour Clock (Math Is Fun)
• The 24 Hour Clock (Flash Application)
• Time Tools: 24hour to the Minute (The Learning Federation) – This is more aimed at children learning the 12 and 24 hour clocks, but it works with both.
• 24 Hour Clock (Study Stack)
• 12 Hour and 24 Hour Clocks