What do the Z, I, and P in “ZIP code” stand for? And what do the numbers represent?

It’s a hectic time of year for the U.S. Postal Service. Those packages you ordered on Cyber Monday are steadily arriving. You’re probably even receiving a few holiday greetings the old-fashioned way — snail mail.

The half million employees who work for the USPS rely heavily on the five- or nine-digit ZIP codes for efficient and reliable mail delivery. So, it makes sense that the term “ZIP code” would be related to being zippy, which means “lively” or “peppy.”

“ZIP” is actually an acronym for Zone Improvement Plan. However, the USPS intentionally chose the acronym to indicate that mail travels more quickly when senders mark the postal code on their packages and envelopes.

The general system of ZIP codes used today was implemented in 1963. Prior to this system, the USPS used a system of postal zones, which was only applicable to large cities. This is where the “improvement” part comes into play.

The basic ZIP code has five digits. The first three digits refer to a sectional center facility (or SCF), what is basically a network of super post offices. All of the post offices that have those three digits in their ZIP code have their mail sorted and processed by the same SCF.  The last two numbers designate the specific post office within an SCF’s territory.

In the 1980s a new system was introduced called ZIP+4. Four additional digits (with a hyphen) were added to the basic code. This allowed senders to indicate an even more precise location, such as a particular block or apartment building. The rise in post office boxes also made this greater level of precision necessary.

Here’s one more postal term to file away: Postnet. The Postnet is a ZIP code translated into a barcode and printed on a piece of mail. The Postnet makes it more efficient for automated machines to sort mail.

Now that you have command of the ZIP code, try the challenge of understanding how to read a barcode. Be warned; it’s not easy. Here’s our explanation.


  1. sulata kumari panigrahi -  November 19, 2015 - 12:48 am

    sir my dactmant recive

  2. saad khan -  February 9, 2015 - 7:23 pm

    I’m a student of Punjab University but I want to know, What is the zip code use and main role in Pakistan and in all over the other Asian countries?

  3. Carissa -  December 26, 2010 - 8:07 am

    Wow, it seems that I often learn just as much from the comments as I do from the article, if not more. It blows my mind to think that at one time, postal codes were just two digits!

  4. Who'da'thought -  December 20, 2010 - 7:17 am

    I have Zip+4 put on all my mail.
    Out post office has many times “lost” our mail without it, including statements from Credit Card companies. Arrgh!
    But now that I pay online, that isn’t much of an issue.

  5. Dwayne McCoy -  December 19, 2010 - 8:40 am

    The postulations set forth are haphazard at best and scurrilous at worst…

  6. thebluebird11 -  December 19, 2010 - 7:49 am

    I didn’t realize that ZIP codes go back to 1963, at which time I was about 5. I still remember “zones” quite well, and even at that young age I was very conscious of addressing birthday and holiday cards to my grandparents, whose zone was 30 (as in Brookly 30, NY). In those days, the zone went in between the city and the state, not after, as the ZIP code does. Amazing little trivia that I can remember from 40+ years ago, when I can’t remember where I put my glasses LOL

  7. john rhea -  December 19, 2010 - 4:23 am

    I always thought it stood for Zoo is Prison, but what do I know, I’m just a po’ colored boy…

  8. C. Jean Brown, PhD -  December 18, 2010 - 11:59 pm

    I still have the paperwork left at my house in early 1963 informing us that our zone would change! It went from 02 to 39202. The hardest thing for us was to remember to write it AFTER the state instead of between the city & state. I just checked the cedar chest and it was originally called zoning improvement plan. So, Kelli, you are right!

  9. Curly -  December 18, 2010 - 5:45 pm

    @Bryan H. Allen and Kelli:

    [An acronym formed from Zone Improvement Program ]
    Encarta ® World English Dictionary © & (P) 1998-2004 Microsoft Corporation. All rights reserved.

    • HGHansen -  January 7, 2015 - 6:01 pm

      I’m recalling that P means program, not plan.

  10. boosielove -  December 18, 2010 - 2:11 pm

    Thanks Cyberquill you teach me alot of interesting things :)

  11. pissed -  December 18, 2010 - 1:49 pm

    @ Dictionary.com

    please remove the AWAZ DO advt. from the website…or atleast stop the knocking sound…
    it is bloodyy irritating…

  12. sherryyu -  December 18, 2010 - 1:10 pm

    wow never in my life had i learned that

  13. kewlkiwi -  December 18, 2010 - 11:17 am

    …..sectional center facility (or SCF), what is basically…

  14. Laurencia -  December 18, 2010 - 9:01 am

    I think the ZIP need some further improvement. A package was mailed to me on Dec 4th ( from Oregon) and I still have not received it. It is the 18th today. It has the ZIP code on it…..

  15. AriesSpirit -  December 18, 2010 - 4:17 am

    Back here in South Africa it’s called the postal code.

  16. Joey -  December 17, 2010 - 6:27 pm

    “The B, A, and R in barcode stand for Beer And Rum”

    No, they don’t.

  17. grainy screen -  December 17, 2010 - 6:24 pm

    black and white, convex and concave in the flat sheet, a body materialized without a ram, and today is a perfect laundry Saturday.

  18. Cyberquill -  December 17, 2010 - 5:09 pm

    The B, A, and R in barcode stand for Beer And Rum, because that’s what is served at a bar.

  19. Mr. Raymond Kenneth Petry -  December 17, 2010 - 12:49 pm

    The ZIP+4 has ambiguous coding: The same address in a condominium can be identified by its building ‘+4′ or its floor ‘+4′– two different ‘+4′s.

  20. S. Cline -  December 17, 2010 - 12:20 pm

    Oddly enough, most businesses don’t want the +4 part of the zip. I know mine, but most of the time, it either doesn’t go in or triggers an error. Cyber Monday emphasized that this still continues.

  21. Kelli -  December 17, 2010 - 11:00 am

    And I’ve always heard it was ZonING Improvement Plan.

    The evidence is buried in the original post office documentation from the 50s and 60s. I think I can live with not knowing!

  22. Bryan H. Allen -  December 17, 2010 - 10:32 am

    Zone Improvement Plan or Zonal Improvement Plan? I read the latter first, years ago. Permissive English grammar allows both variants, but factually, historically, which was original? I suspend all further effort to resolve that one. O trivia collectors, where is your evidence?


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