What are the three lines of a PO Box letter address?
The recipient's name, then PO BOX followed by the number, then city, state and ZIP together on the last line. USPS Publication 28 standardizes the box line itself as PO BOX ##.
Envelope basics
How to address a letter to a PO Box
A PO Box letter drops to three lines and leaves the street address out entirely: the recipient's name, "PO BOX" and the number, then city, state and ZIP. Publication 28 standardizes the box line itself as PO BOX ##, and that is the whole difference from a street-address envelope, read 2026-09-01.
Pub 28, citedThree-line formatRead 2026-09-01
No street line to fill in
The box number does the job a street address does everywhere else.
The three lines, and nothing more
Publication 28 fixes the middle line's wording exactly: "The Post Office Box address on a mailpiece must be standardized as follows: PO BOX ##," read 2026-09-01. Around that, the block follows the same recipient / delivery / last-line shape used on any envelope.
M RIVERA
PO BOX 4471
COLUMBUS OH 43215
PO BOX 4471
COLUMBUS OH 43215
That is the complete address. Nothing about the Post Office's own street sits in this block by default — the box number is doing the job a street number does everywhere else, and adding one on your own does not help the piece move faster.
Where a street address does belong
Some Post Offices let a box holder add their own street addressing on top of the box number. Publication 28 describes it as an option, not a default, read 2026-09-01: "PO Box services in some locations allow for an option to use the Post Office street address for the mailing address, along with the PO Box number preceded by a "#" sign or "UNIT" designation."
In practice that means the box holder has to tell you the street form exists and give you the exact line, "#" and number or "UNIT" and number, rather than you working it out. Absent that, "PO BOX ##" is the correct and complete second line every time.
A PMB is not a PO Box
A private mailbox at a commercial mail receiving agency looks similar on paper but is a different product entirely, and Publication 28 keeps the wording from crossing over, read 2026-09-01: "Only the Postal Service is entitled to provide delivery to a PO Box," so a private mailbox address uses PMB or a "#" instead.
| Box type | Who provides it | Line format |
|---|---|---|
| PO Box | USPS itself | PO BOX ## |
| Private mailbox (PMB) | A commercial mail receiving agency | PMB ## or # ##, never the words PO Box |
Publication 28 also allows a PMB address to run three or four lines, but requires the three-line form when the mail receiving agency's own street address already carries a suite or unit number of its own — otherwise the PMB number and the agency's own secondary address collide on the same line.
Common questions
Do I need a street address for a PO Box letter?
No, not by default. The Post Office's own street address only enters the picture where that location offers PO Box Street Addressing, an option a box holder has to have and give you, not something you add on your own.
Is a PMB the same thing as a PO Box on the envelope?
No, and the wording cannot cross over. Publication 28 reserves PO BOX for boxes the Postal Service itself rents out; a private mailbox at a commercial mail receiving agency uses PMB or a # sign instead, never the words PO Box.
What if the box number has a leading zero?
Write it as given. Publication 28's own systems represent a significant leading zero with a hyphen internally and convert it back to a zero on the printed piece, so the number a box holder gives you is the one to use.
Can I write DRAWER or LOCKBOX instead of PO BOX?
Change it to PO BOX. Publication 28 treats CALLER, FIRM CALLER, BIN, LOCKBOX and DRAWER as older labels for the same thing and standardizes all of them to PO BOX on the piece.
Where this format comes from
- USPS Publication 28, Section 281 — the PO BOX ## format rule. Read 2026-09-01.
- USPS Publication 28, Sections 282-283 — leading zero handling and CALLER/BIN/DRAWER-style relabeling. Read 2026-09-01.
- USPS Publication 28, Section 284 — PO Box Street Addressing. Read 2026-09-01.
- USPS Publication 28, Section 285 — Private Mailbox (PMB) addresses and the PO Box distinction. Read 2026-09-01.
These sections govern format, not delivery eligibility. What USPS will actually deliver to a box, and what happens when a parcel outgrows it, is a separate question our PO Box shipping guide covers with priced examples.