It’s About Time: Clock Time

In a recent Keys to Error-Free Writing class, participants wanted to know how to render clock time. A.M. or a.m.? PM or pm? 24-hour clock? 12-hour clock? Mention time zones or leave them out? Refer to GMT (Greenwich Mean Time)?

These questions rarely came up a few years ago. But now we write for the globe, and it is essential to write about time in a way that our global readers will understand.

Because Microsoft communicates successfully around the globe, I checked the Microsoft Manual of Style for Technical Publications for ideas on writing about time. Here are rules based on that reference manual:

  1. When you are writing for a global audience, avoid using a.m. and p.m. Instead use a 24-hour clock format. For example, for 2 p.m. use 14:00. For noon, use 12:00; for midnight, use 00:00 or simply midnight.
  2. Along with the time, provide the time zone, such as Eastern Time or Pacific Time for a North American audience. If you are writing for an international audience, give Coordinated Universal Time. If your readers may not recognize Coordinated Universal Time, which is the new accepted name for Greenwich Mean Time, you may include Greenwich Mean Time in parentheses after Coordinated Universal Time. Coordinated Universal Time is 5 hours later than North America’s Eastern Standard Time. It is not affected by Daylight Saving Time.
  3. Do not abbreviate the names of time zones (PT, ET) unless space limitations require you to do so. Coordinated Universal Time is abbreviated UTCnot CUT.
  4. For an international time zone that does not have a name, use an expression like this: UTC+7. (This time zone is 7 hours ahead of Coordinated Universal Time.)

Do these rules sound confusing? Communicating about time has become more challenging as the world has grown smaller. My personal rule is this: Communicate first for your primary audience, and add information for your readers around the globe. For example:

  • If you are scheduling a webcast for an international audience, most of whom are in the United States and Canada, announce the time this way:

The webcast begins at 17:00 Pacific Time (UTC-8).

  • If you are scheduling the same program for an international audience, most of whom are in Australia (which, like North America, has an Eastern Time zone), announce the time this way:

The webcast begins at 8:00 Eastern Time (UTC+10).

Please send your stories or suggestions for communicating about time.

Alternate search spellings: Greenwhich, interntional, tehcnical, cooredinated, cooreidnated, Paicif, Paicifc, UCT


  1. Please advise on the correct writing of military time.

    During the hours of 0800 through 1500 hours.

    Should the second “hours” be in the sentence or leave it out?

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