What do Zip Code numbers mean?

Summary:How does the mail reach over 141 million homes and businesses each day? What is your 9 digit zip code and what does it mean?

A lot of people complain when, every year or so, the price of postage goes up three or four cents, but I for one think it’s pretty cool that you can slap the representation of 39 cents on an envelope and have it appear in whatever city you’d like it to go in just a few days. Sure, our letter carriers are awesome and the sorting machines can do more and do it faster than ever, but what it really comes down to is five little numbers: our Zoning Improvement Plan – or ZIP – codes.


Despite the advancement of airline transport, in the 1930s the bulk of our mail was still moved primarily by rail. While it wasn’t especially speedy or efficient, it didn’t really have to be as during that time mail was used primarily for social purposes. By the early 1960s the process had been refined considerably, using significantly fewer trains and taking far less time than it had in the past. The mid 60s mail gave way to the birth of the computers and businesses and government comprised over 80% of our mail with centralized billing, banking, social security checks, magazine subscriptions, and other mail – some good, some bad – that our boxes are now flooded with on a daily basis.

Enter the Presidential appointed Advisory Board of the Post Office Department.

In 1962, after a detailed study of the mechanization problems of our mail system it was decided that a coding system was desperately needed to handle the huge increase in volume the postal system had undergone in the previous 30 years. After several attempts, on April 30, 1963 the system that we know today as the five-digit United States zip code was born. In an unusual demonstration of speed and efficiency, by July of that same year the U.S. government was able to assign every address in the country their own numbers.

The U.S. Postal Service works roughly like this: you drop your mail, it goes to a regional center. It then goes to one of the 85 urban transportation centers set up just outside of our major cities (so as not to congest nor get delayed by traffic). These offices act as a hub for 522 satellite centers that then serve anywhere from 40 to 150 smaller offices. Zip codes get assigned according to what is called the “Metro System.” The first digit representing the region, with “0” starting in the Northeast and “9” in the West. The next two digits are associated with the urban transportation center, and the final two digits pinpoint the exact post office or zones.

But this is the federal government we’re talking about here. Could it really be this easy? Well, yes and no. For a while.

According to the USPS, hundreds of millions of pieces of mail reach over 141 million homes and businesses each day – which is a lot of mail relying on five little numbers. To make mail faster to sort, face, and cancel, four more numbers following a hyphen were added to the already existing five. These digit zip codes have reduced the number of times a piece of mail has to be handled by a human being, thus reducing the chance of errors during delivery and enabling us all to get our mail faster.

Even so, ask someone their nine digit zip code and they’ll probably laugh a little – at least they did when I asked. But if you like to be the epitome of efficiency, or you just have nothing to do, then you can go to the USPS website and look up your 9 digit zip at www.usps.com.



Author: Chuck Eglinton