US ZIP Code Validator

A US ZIP Code validator that goes beyond a simple digit-count check. Enter any 5-digit ZIP or full 9-digit ZIP+4 and the tool runs three real checks in your browser: format validation, USPS Sectional Center Facility (SCF) prefix assignment, and ZIP+4 add-on plausibility — then tells you which US state or territory the prefix belongs to. Everything is instant and 100% private.

How it works

USPS organises delivery addresses into a hierarchy. The 5-digit ZIP code breaks down as follows:

• Digit 1 — National area (0 = Northeast, 9 = West/Pacific)
• Digits 1-3 — The Sectional Center Facility (SCF) prefix, which identifies the regional sorting hub
• Digits 4-5 — The post office or delivery area within that SCF
• Digits 6-9 (ZIP+4 only) — A specific delivery segment such as a city block, a floor of a building, or a PO Box range

The validator applies the following layers in order:

1. Format — only digits and one optional hyphen after position 5 are permitted. Inputs like 1000A or 10001-234 (too short an add-on) are immediately rejected with a clear explanation.
2. Length — ZIP-5 must be exactly 5 digits; ZIP+4 must be exactly 9 (written with or without the separating hyphen).
3. Prefix assignment — the first 3 digits are looked up in a table of all USPS-assigned SCF ranges. Dozens of 3-digit combinations (such as 000, 099, 213, 269, 343, and many others) have never been issued; the tool flags them so you can spot invented or corrupted codes immediately.
4. State mapping — if the prefix is assigned, the tool reports the state or territory (including military mail codes AA, AE, AP and territories like GU for Guam).
5. ZIP+4 add-on — the 4-digit suffix must be 0001–9999. The value 0000 is not issued by USPS and is rejected with a specific message.

Example

Validate 10001-2345 (a Manhattan ZIP+4):

• Format — pass (digits only, hyphen in correct position)
• Length — pass (9 digits)
• Prefix 100 — assigned, maps to New York (NY)
• Add-on 2345 — in the valid range 0001–9999, so it passes

Result: Valid ZIP+4, state New York (NY).

Now try 00000:

• Prefix 000 is in the USPS unassigned list — this code has never been issued.

Result: Invalid, with the message “Prefix 000 is an unassigned USPS range.”

Every check runs locally in your browser — no data is sent anywhere.