Date and Time Notation

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[Summary of ISO 8601] [Campaign for Use of ISO 8601]

Although there is a metric unit of time (the second), there is no such thing as metric time. There have been several proposals, over the years, to decimalize the way we express time — at least for the hours, minutes and seconds in a day. None of them ever caught on.

The International Organization for Standardization (ISO) has, however, published a standard for date and time notation. That standard is ISO 8601. It provides a consistent and logical method for expressing year, month, day, hour, minute and second. It avoids the confusion with respect to the difference between US practice (month, day, year) and non-US practice (day, month, year) and, by using a 24-hour clock, avoids ambiguities and the issue of the use of a.m. or p.m. for noon and midnight.

The ISO 8601 standard applies only to dates and/or times that are written in all-numeric form. For dates, ISO 8601 provides no guidance for the non-ambiguous case where the month is spelled out ("long date" format). 

In the United States, implementation of ISO 8601 in new documents and systems is rare, even though the capability to use it already exists in PC operating systems, such as Windows, where the ISO 8601 format is an implicitly selectable option via the Date and Time tabs of the Regional Settings Control Panel applet. For instructions for Windows or for the Macintosh, click on one of the following:

Markus Kuhn, of Cambridge University, has a very informative page, summarizing and clarifying the ISO 8601 standard.

Here, Steve Adams makes a very emphatic case for the adoption of the ISO 8601 standard. He emphasizes, though, that he is not campaigning to change the way we express dates in an informal context (e.g., in speech).

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On this page
[Summary of ISO 8601] [Campaign for Use of ISO 8601]