USMA logo

International date and time notation


The International Organization for Standardization (ISO) sets standards that harmonize measuring and other practices for everybody worldwide. One of those standards is ISO-8601 that specifies the international date and time notation/convention. This notation bridges the various non-standard dating formats used by nations by standardizing the year-month-day sequence in particular. Otherwise a date written in the form 01/02/03 could represent January 2, 2003 in the U.S., or 1 February 2003 in Europe and most of the rest of the world.


A short overview of ISO-8601

DATE: For date, ISO-8601 recommends the year, month, and day be written with hyphens as YYYY-MM-DD. The standard allows other options that, however, are uncommon worldwide. (There is no option to the sequence of the elements, though.) Examples of the predominating notations are:

2003-01-31

If only the month or only the year is of concern, 2003-01 or 2003 is also appropriate.

This format should be used in all technical communication (i.e., drawings, reports, test data, procedures, specifications, manuals, purchase orders, instructions). For non-technical documents (personal letters, memos, well wishes, announcements) that are intended to be read in the U.S. or another English-speaking country only, the month is sometimes spelled out. This is to eliminate the possibility of confusion and help laymen accept the novelty. Thus, in non-technical communication to and within English speaking countries the data can optionally be written as:

2003 Jan 31

Notice that this non-ISO format shows no hyphens, and that the month is indicated by the first three letters of the name, the first letter capitalized, and no period at the end.


TIME: Concerning the time of the day, the international standard sequence and notation is HH:MM:SS.ms…., and the hour is on the 24/day basis. For example:

23:59:59.999

which means a millisecond before midnight. Midnight can be 24:00 or 00.00. Only the 00:00 is to be used when by itself (such as digital clocks), while in combination with the date, either is appropriate as is shown next.


DAY AND TIME COMBINATION: The date and time combination is written divided by a space (a tap on the space-bar). As an example, the end of the month is:

2003-01-31 24:00

This midnight can also be written as 2003-02-01 00:00

In data processing, where the date and time information must be stored as single data field, the standard recommends inserting the character "T" between the date and time. For example:

20030131T235959


Setting your Personal Computer (PC) for ISO-8601

TYPING DATE, TIME, AND NUMBERS: It is recommended that you set up your PC to automatically display the worldwide convention for date, and time, and numbers. The convention stipulates the following:

Below is a method for setting one's PC to communicate date and time the way it is becoming understood in most of the world, including in the U.S. Setting your PC according to the steps below will also save you typing time from that point on. Following the entries keep in mind that many are case sensitive.

Troubleshooting: If you do not get the above format with MS Word's Header/Footer when you click on its date and time icons, or if you do not get the automatic date entry to reflect the above, do the following:

This procedure uses MS Windows and MS Word terminology that has become common in the last decade. Older software versions may use different terminology (for example "style" instead of the above "format") but the essence of the procedure is the same in most versions.


This summary of date and time formatting information was provided by USMA member Stan Jakuba.

For additional information on the ISO-8601 standard, see Markus Kuhn's Website on International standard date and time notation


Back to USMA home.



Copyright © 2004, U.S. Metric Association (USMA), Inc. All rights reserved.
Web hosting courtesy of Colorado State University.
Website maintained by USMA Webmaster
Updated: 2004-10-11