ZIP+4 Codes | What are they and How do I find mine?

USPS 5-digit Zip Codes

USPS five-digit zip codes are the zip codes you are familiar with. Examples are 92019 or 84604. The 5 digit zip code most commonly indicates a destination post office.

Here’s how it works:

• A postal carrier collects your letter from the box along with the rest of the mail and takes it to the post office. There, all of the mail is placed on a truck and taken to a mail processing plant.
• At the mail processing plant, machines separate mail by shape and size. They also orient the packages so their addresses are right-side up and facing the same direction. Your letter gets its postmark, and machines print cancellation lines across postage stamps to prevent them from being reused.
• A unique bar code is imprinted on the back of each piece of mail. An optical scanner scans the address, and then a bar code representing the specific address is sprayed on the front of the envelope. If the scanner can't read the address, the letter is manually sorted.
• Other processing machines read the bar codes and direct the letters into bins based on ZIP codes — this indicates the next processing plant, in the region where the letter will ultimately be delivered. (Each post office is served by a mail processing plant.) From the bins, the letters are sorted into trays by ZIP code and flown or trucked to the next processing.
• At the final processing plant, sorting machines read the bar codes and sort the letters by carrier and into delivery order for that carrier.
• The letters are taken to the individual post offices, and the carriers load the trays into their individual vehicles for final delivery.

Demystifying ZIP Code Lookup Tool: Beyond Just Delivering Mail

Zip+4 Codes - 4 extra digits

A ZIP+4 code uses the basic five-digit code plus four additional digits to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, a post office box, or a specific delivery route — meaning the actual path the mail truck would travel could have changed.

Because they are based on delivery routes instead of more permanent boundaries, the last 4 digits of a complete ZIP code can change often. Five-digit ZIP codes also change, but they do so infrequently. Not so for ZIP+4. The +4 on a ZIP code can be changed as frequently as once a month, based on things like how many postal employees are working, who is working what route, etc.

A ZIP code is a postal code used by the United States Postal Service (USPS) in a system it introduced in 1963. An extended ZIP+4 code was introduced in 1983 which includes the five digits of the ZIP code, followed by a hyphen and four additional digits that reference a more specific location. However, initial attempts to promote universal use of the new format met with public resistance, and today the +4 code is not required. In general, mail is read by a multiline optical character reader (MLOCR) that almost instantly determines the correct ZIP+4 code from the address — along with the even more specific delivery point — and sprays an Intelligent Mail barcode (IM) on the face of the mail piece that corresponds to 11 digits — nine for the ZIP+4 code and two for the delivery point.