1 Telling Time: the 24-Hour Clock

What Time is It?

In North America, most citizens tell time using the 12-hour clock. In this system, each number from one to twelve gets used twice each day to tell the hour. The code “a.m.” is added at the end to designate morning hours (from midnight to noon), and “p.m.” is used to designate afternoon, evening, and night-time hours. These codes come from Latin expressions meaning “ante meridiem” (before mid-day) and “post meridiem” (after mid-day).

For example, how is 8:00 in the morning commonly written?

8:00 a.m.

How would you read this out loud?

Someone saying this time out loud would say “eight A M.” If it was clear from context that they were talking about morning, they might simply say, “eight o’clock,” or simply, “eight.” If they were communicating about 8:00 in the evening, they would write it as “8:00 p.m.” If speaking, they might again simply say “eight o’clock” or “eight,” and trust that it were clear from context that they were referring to the evening.

But what if it were  not clear from context? Or what if someone’s messy handwriting makes the “a” in “a.m.” look a little too close to the “p” in “p.m.”? How valuable would a witness statement or investigator’s notes be if their observations were off by a full twelve hours?

In law enforcement and investigations, precision and accuracy matter! There is too much margin for error when we repeat numbers like we do in the a.m./p.m. system. To avoid these mix-ups, people in law enforcement use the 24-hour clock. This system isn’t exclusive to law enforcement. People in the military, medical professionals, and even ordinary citizens in many parts of the world use the 24-clock as their default way of telling time.

With the 24-hour clock, the numbers don’t reset after 12:00 noon. Each hour of the day and night gets its own number. This means that the hour that comes after 12:00 noon isn’t 1:00 p.m. … it’s 1300h! 2:00 p.m. is 1400h, 3:00 p.m. is 1500h, and so on. Counting the hours this way eliminates the margin for error created in the a.m./p.m. system.

How do you actually say these times out loud?

How would you say 1800h out loud? It could be said as:

• eighteen hundred hours; or
• one-eight-zero-zero hours.

How about 0350h? You could say:

• oh-three-hundred-fifty hours; or
• zero-three-five-zero hours.

Either way, do not drop the zero (or, if speaking, the “oh”) at the start of the number.

Different communities often develop their own preferred way of saying things. For example, when it’s really early in the morning, some military units use the slang expression “zero dark” to represent the “00–” in the first hours of the morning. Have you ever heard of the movie Zero Dark Thirty? That title refers to the time at which the story’s main incident happened: 0030h (12:30 a.m.).

Since there is no single, universal way of saying the time out loud with the 24-hour clock, your best bet is to know some options, keep your ears open for how people around you speak, and go with the flow. Remember your main purpose: to communicate in such a way that the other person understands clearly.

Need more practice? Review one or both of the videos below: