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When looking at postal codes around the world, there are cases where two different cities are served by the same postal code. For example, the zip code 94608 in California is used for both Emeryville and parts of Oakland.

ZIP codes can and do cross state lines (rarely, but just enough to cause some problems and confusion), county lines (about 10% of ZIPs are in more than one county), political jurisdictions (cities, congressional districts), metro areas, etc.

ZIP Code? or ZIP+4® does not match City/State. If undeliverable there, it is forwarded to the Post Office as stated by city and state.

So what do the extra numbers mean? These last 4 digits represent specific delivery routes within delivery areas. This extra detail means an even more precise matching to a more granular level. It could represent a handful of houses on one side of a street, or even a single building that receives a high volume of mail.

The five-digit code which initially specified an area or a part of a town was no longer accurate or efficient enough. So, USPS created 9-digit ZIP Codes to ensure fast and accurate mailings.

No! Just use the first five digits. USPS computers will read the address then look it up and supply all eleven numbers needed for delivery and print a barcode containing all those numbers. Writing any more than the first five digits will not speed up delivery at all.

So what do the extra numbers mean? These last 4 digits represent specific delivery routes within delivery areas. This extra detail means an even more precise matching to a more granular level. It could represent a handful of houses on one side of a street, or even a single building that receives a high volume of mail.