Apartment & PO Box Address Format: How USPS Wants It Written

USPS sorting equipment reads a specific block of the envelope, and a missing apartment number is the most common reason a correctly stamped letter still comes back. The format is simple once you know the order:

JANE DOE
APT 4B
123 MAIN ST
SPRINGFIELD IL 62704-1234

That is it — recipient name, unit number, street address, then city, state, and ZIP+4.

The four lines, in order

Line	What goes on it	Example
1	Recipient’s full name or company name	JANE DOE
2	Apartment, suite, unit, or floor	APT 4B / STE 200 / UNIT 12
3	Street address	123 MAIN ST
4	City, state abbreviation, ZIP+4	SPRINGFIELD IL 62704-1234

The unit number can also sit at the end of the street line — `123 MAIN ST APT 4B` — and USPS will read either. Putting it on its own line is easier to read and less likely to be truncated by a printer.

Formatting rules that prevent returns

• Use capital letters. No commas, no periods.
• Use the official two-letter state abbreviation (IL not Ill., CA not Cal.).
• Include ZIP+4. It narrows delivery to a block or building and speeds sorting. Look up any address with the USPS ZIP Code lookup tool.
• Use USPS-standard street suffixes — ST, AVE, RD, BLVD, DR, LN, CT, PL.
• Spell the unit type consistently: APT, STE, UNIT, RM, FL, BLDG, BASEMENT, TRAILER.
• Leave the bottom of the envelope clear. USPS prints its routing barcode in the lower area; keep roughly the bottom 5/8″ free of text and decorations.
• Keep the address in the lower center, with the return address in the top-left corner and postage in the top-right.

PO Box addresses

A PO Box replaces the street line entirely:

JANE DOE

PO BOX 1234

SPRINGFIELD IL 62705-1234

If you include both a street address and a PO Box, USPS delivers to the PO Box — which is fine if that is what you want, and confusing if it is not. Pick one.

## Business mail and attention lines

For mail to a company, put the person or department on the first line and the company on the second:

ACCOUNTS PAYABLE

MIDWEST SUPPLY CO

STE 200

4500 INDUSTRIAL PKWY

SPRINGFIELD IL 62704-1234

An `ATTN:` line works the same way — `ATTN: JANE DOE` above the company name.

Military and diplomatic mail (APO/FPO/DPO)

These follow their own rules and get them wrong surprisingly often:

SEAMAN JOSEPH SMITH
UNIT 100100 BOX 4120
FPO AP 96691

• Do not write the city or country name. Doing so can route the letter into a foreign postal network.
• Include the unit and box numbers when assigned.
• Use the correct “state”: AA (Armed Forces Americas), AE (Europe/Africa/Middle East), AP (Pacific).

The five mistakes that send mail back

1. No apartment number — the letter reaches the building and stops there.
2. A wrong or outdated ZIP code — verify multi-building complexes with the USPS ZIP Code lookup.
3. Handwriting that machines cannot read — print addresses for anything important, or write in neat capitals.
4. Decorations or dark envelopes in the address area — low contrast confuses the scanners.
5. Using the old city name after an address change — USPS standardizes addresses; use its current form.

Frequently asked questions

Does the apartment number go on its own line?

Either way works. Its own line is clearer: `APT 4B` above the street address.

Do I need ZIP+4?

It is not required, but it improves accuracy and is free to look up. For apartment buildings and large offices it meaningfully reduces misdelivery.

How do I write “suite” — STE or SUITE?

Both are read. USPS prefers the standard abbreviation STE.

Can I use a PO Box as a return address?

Yes. Just write it the same way you would as a delivery address.

Getting the address right is half the battle

The other half is having the right postage on hand. If you mail invoices, statements, or letters regularly, keeping a working stock of discount Forever stamps — say 2013 Flags — means a format fix never turns into a trip to the Post Office. Renting a PO Box? USPS explains the options on its PO Box page. For heavier business mail, read How to Buy Stamps, Where to Buy Stamps, or buy Forever stamps in bulk.

Need the stamps? Browse our full shop of discount USPS Forever stamps.