US ZIP Code Guide: How 5-Digit ZIP Codes Work, with Examples
2026-08-18 · US Address Generator
When you fill in a US address, the ZIP Code is the field most likely to trip you up. It is not a random five-digit string: the leading digits map to large regions and major cities, while the trailing digits narrow down to a delivery area. Here is how it all fits together.
How a 5-digit ZIP Code is structured
- First digit: a broad region. ZIPs starting with 0 cover the Northeast, while 9 covers the West Coast.
- Second and third digits: a sectional center or a major city.
- Fourth and fifth digits: a smaller delivery area, post office or group of blocks.
For example, in 90210 the 9 marks the West, 902 points to Beverly Hills in California, and the final 10 narrows it to a specific delivery area.
What ZIP+4 means
Some forms ask for ZIP+4, such as 90001-1234. The extra four digits can identify a single building, a block segment or a large organization. For almost every everyday form, the basic five digits are enough — USPS adds the +4 automatically when it standardizes an address.
Examples from major cities
| ZIP | City | Note |
|---|---|---|
| 10001 | New York (Manhattan) | 1 prefix, Northeast region |
| 60601 | Chicago downtown | 6 prefix, Midwest |
| 90001 | Los Angeles | 9 prefix, West Coast |
| 94105 | San Francisco | SOMA / Bay Area |
| 33101 | Miami | 3 prefix, Southeast |
| 98101 | Seattle downtown | 9 prefix, Northwest |
How to look up a ZIP Code
The authoritative source is the ZIP Code Lookup on the USPS website. If you want the reverse direction — enter a ZIP and see which state and city it belongs to — try the ZIP database tool on this site.
Why big cities have so many ZIPs
New York City alone has more than 200 ZIP codes: the denser the mail volume, the finer the split. Looking up a city from a ZIP works fine; guessing a ZIP from a city does not. Always look it up.
Three common mistakes
- State and ZIP that disagree: ZIP prefixes are tied to states. A California address with a 1-prefixed ZIP will fail validation.
- Wrong number of digits: US ZIPs have exactly five digits — not six, not four.
- Expecting door-level precision: a ZIP usually covers a group of streets, never a single doorway.
To see how ZIP, state and city fit together, generate a few sample addresses in the US address generator, or revisit the US address format guide.