Standards
USPS envelope addressing standards
USPS Publication 28 is the official rulebook USPS uses to define a standardized address. It covers the delivery line, the last line, secondary address unit designators like APT and STE, directionals, numeric street names, and specialized formats like rural routes and PO Boxes, organized into numbered sections such as Section 213 for unit designators and Section 235 for numeric street names.
Checked July 30, 2026/8 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page6 sections
Almost every page on this site mentions USPS Publication 28 somewhere, and most addressing advice anywhere online does the same, usually as a vague appeal to authority rather than an actual citation. This page is the difference: the real section numbers, the real rule language, organized the way USPS itself organizes it.
Publication 28 is not a short document, and nobody needs to read all of it. But knowing that the same-line apartment rule lives in Section 213, or that numeric street names have their own specific rule in Section 235, turns a vague “USPS says so” into something you can actually go verify.
Step by step
Start with what "standardized" actually means
USPS defines a standardized address as one that includes every required element and uses the Postal Service standard abbreviations, quoted directly from Section 21. Everything else in Publication 28 is really just the specifics of what those elements and abbreviations are.
The last line, Section 22
City, state, and ZIP code, in that order, with the two-letter state abbreviation and no punctuation. This is the line USPS equipment reads first, from the bottom up.
The delivery address line, Section 23
The street number, street name, any directionals, and the suffix. This section also covers numeric street names specifically.
JORDAN REYES1420 7TH STDENVER CO 80202CorrectA numeric street name, written exactly as USPS ZIP+4 records hold it. Secondary address unit designators, Section 213
APT, STE, UNIT, FL, and the rest, covered in the same section referenced throughout this site apartment page. This is the specific subsection to cite if you ever need to point to a source for the same-line placement rule.
Specialized address types, Sections 24 through 29
Rural routes, highway contract routes, general delivery, USPS-owned addresses, PO Boxes, and Puerto Rico addresses each get their own numbered section, since each has formatting quirks the general rules do not fully cover.
Quick reference
| Section | Covers |
|---|---|
| 21 General | Definitions, format, secondary unit designators, attention lines |
| 213 | Secondary address unit designators (APT, STE, UNIT, and more) |
| 214 | Attention line format |
| 22 Last Line | City, state, ZIP formatting rules |
| 225 | Military address formatting within the last line |
| 23 Delivery Line | Street number, name, directionals, suffixes |
| 235 | Numeric street name formatting |
| 24 Rural Route | RR and box number format |
| 25 Highway Contract Route | HC and box number format |
| 28 PO Box | Post office box formatting |
Special cases
The rule above covers most people. Here is what changes for the rest.
When should a numeric street name be spelled out instead of written as a number?
Publication 28, Section 235, states that numeric street names should be written exactly as they appear in the USPS ZIP+4 file, which is usually the numeral form, 7TH ST rather than SEVENTH ST. The one exception is when a delivery area has duplicate street names and the spelled-out version is specifically what distinguishes the correct address from the wrong one. Outside that specific case, the numeral form is standard.
What is a mailstop code, and is it new?
A mailstop code is a business addressing element, added to Publication 28 as Section 327 effective October 2023, used mainly by large organizations to route mail to a specific internal location within a building or campus once it arrives. It is recent enough that a lot of general addressing advice has not caught up with it, and it functions similarly to an attention line but is specifically standardized for large-scale business mail routing rather than routing to an individual.
Key terms on this page
- Standardized address
- USPS official term for an address containing every required element, written using the Postal Service standard abbreviations, as defined in Publication 28 Section 21.
- ZIP+4 file
- The USPS database of every standardized deliverable address in the country, including the exact spelling and abbreviation format each address should use.
- Delivery address line
- The line containing the street number, street name, directional, and suffix, covered under Publication 28 Section 23.
- Mailstop code
- A business addressing element added in 2023, used to route mail to a specific location within a large organization once it has already been delivered to the building.