US Address Format Explained: ZIP Codes, States & USPS Rules

A standard US mailing address has three core lines, in this order:

1. Recipient — full name or business name
2. Delivery line — house number + street name (+ apartment/unit)
3. Last line — city, two-letter state abbreviation, ZIP code

For example: Sarah Moore · 4967 Lincoln St · New York, NY 10016. USPS prefers everything in capital letters with no punctuation, but normal casing is accepted everywhere in practice.

How ZIP codes work

ZIP stands for Zone Improvement Plan. The five digits narrow down location progressively: the first digit is a broad region (0 = Northeast, 9 = West Coast), digits two and three identify a sectional center, and the last two identify the delivery post office. ZIP+4 (e.g. 10016-3556) adds a specific block or building — optional on forms, used by USPS for sorting.

What address validation actually checks

Most e-commerce and sign-up forms don't verify that a house number exists. They check internal consistency:

• Is the state abbreviation valid (NY, CA, TX…)?
• Does the ZIP code fall in that state's range?
• Does the ZIP match the city name?
• Does the phone area code plausibly match the region?

This is why randomly typed addresses get rejected while properly assembled ones pass. Our US address generator builds every address from a real city with its genuine ZIP codes and area codes, so all four checks succeed.

State abbreviations worth knowing

The USPS two-letter codes are mandatory on the last line: CA (California), NY (New York), TX (Texas), FL (Florida), WA (Washington), IL (Illinois) — and the five sales-tax-free states OR, DE, MT, NH and AK, which we cover in the tax-free states guide.