How to Write an Apartment Address
Put the apartment number at the end of the delivery address line, using the correct designator — APT, STE, UNIT — rather than the # sign. Here are the exact USPS rules, the approved abbreviations, the awkward cases, and why the format matters for mail forwarding, utilities, deliveries, and your movers.
The short answer
Put the apartment number at the end of the delivery address line, using the correct designator — APT, STE, UNIT — rather than the # sign.
Correct format
- Recipient
- JANE SMITH
- Delivery address line
- 1010 HYDE ST APT 4B
- City, state, ZIP
- SAN FRANCISCO CA 94109
That is it. Everything below is the detail for the cases that do not fit the simple version.
Format rules from USPS Publication 28, Section 213: Secondary Address Unit Designators.
The rules, exactly
| Rule | What USPS says |
|---|---|
| Where the unit goes | "The preferred location is at the end of the Delivery Address Line." |
| When it does not fit | Place the secondary address information on the line immediately above the delivery address line. |
| Using the # sign | "The pound sign (#) should not be used as a secondary unit designator if the correct designation, such as APT or STE, is known." |
| If you do use # | "There must be a space between the pound sign and the secondary number." |
The rule about the # sign is the one most people get wrong. 1010 HYDE ST #4B is worse than 1010 HYDE ST APT 4B, and 1010 HYDE ST # 4B is the acceptable version if you use the symbol at all.
The common designators
| Designator | Abbreviation | Example |
|---|---|---|
| Apartment | APT | 1010 HYDE ST APT 4B |
| Suite | STE | 500 MARKET ST STE 1200 |
| Unit | UNIT | 24 OCEAN AVE UNIT C |
| Building | BLDG | 800 BRANNAN ST BLDG 2 |
| Floor | FL | 1 POST ST FL 9 |
| Room | RM | 100 LARKIN ST RM 210 |
| Department | DEPT | 350 MISSION ST DEPT 4 |
The full approved list is in Appendix C2 of Publication 28. Use the designator the building itself uses — if the letterboxes say "Unit", write UNIT.
Formatting the whole address
Getting the designator right matters on moving day too, because it is what the driver reads. California Movers USA confirms the full delivery address, unit included, with the sales specialist before the date is booked — a missing unit number is a common cause of a long carry that ends up on the invoice.
- Line 1 — recipientFull name, as it appears on the mailbox or the lease.
- Line 2 — delivery addressStreet number, street name, then the unit designator and number at the end.
- Line 3 — city, state, ZIPTwo-letter state abbreviation, then the ZIP or ZIP+4.
USPS prefers uppercase, no punctuation, and left alignment for machine reading. Handwritten mail does not have to follow that to be delivered, but a package label should.
The most common failure is not a wrong designator — it is leaving the unit number off entirely. Mail to a large building without a unit number goes back or sits in a pile.
Awkward cases
Long street names. If the whole thing will not fit on one line, put the unit on the line above the street address, not below it.
Two buildings on one lot. BLDG comes before the unit: 800 BRANNAN ST BLDG 2 APT 5.
Basement or garden flats. Use what the building uses. If it is simply "Lower", write it as the unit: 1420 PAGE ST UNIT LOWER.
Letters and numbers. Keep them together as the building lists them: APT 4B, not APT 4 B.
Rural routes and PO boxes. A PO box is not a secondary designator; it replaces the street address entirely.
Deliveries that need a buzzer code. Do not put it in the address. Put it in the delivery instructions field, where the carrier or driver actually reads it.
Why this matters when you move
A wrongly formatted unit number is one of the quieter ways a move goes wrong. It affects more than mail.
- Mail forwarding. A USPS change of address matches on the formatted address. If the format is off, forwarding can fail silently — file it at USPS.
- Utilities. Service is set up per unit. The wrong unit number connects the wrong apartment.
- Deliveries. Furniture, appliances, and anything on a freight schedule will be attempted once and returned.
- Your movers. The delivery address on a bill of lading is what the crew navigates to. A missing unit number costs time on the clock.
- Voter registration and the DMV. Both match on the address of record.
Write your new address out in the correct format once, then copy and paste it everywhere. That one habit prevents most of the problems above.
Where we use it
On a move, the unit number belongs in the written scope, not just in a phone conversation. It determines which door the truck goes to, whether an elevator reservation is needed, and how long the carry is.
When you get a quote from us, the sales specialist confirms the full address including the unit, the floor, and the elevator situation — that is what a dispatcher plans around. See apartment moving for how building access is handled, and pricing for how it affects the estimate.
Related reading: setting up utilities, how to pack for a move, and moving to California if you are arriving from another state.
Questions people ask
Where does the apartment number go?
At the end of the delivery address line: 1010 HYDE ST APT 4B. USPS states this is the preferred location.
Can I use the # sign?
USPS says not to when the correct designator is known. If you do use it, leave a space: # 4B.
What if the address is too long for one line?
Put the unit information on the line immediately above the delivery address line — above, never below.
Is it APT or Apt?
USPS prefers uppercase with no punctuation for automated processing. Either will be delivered by hand; use uppercase on labels.
Do I need ZIP+4?
Not required, but it improves sorting accuracy. USPS has a lookup tool for it.
Where do I put a gate or buzzer code?
In the delivery instructions, not the address. The address line is read by machines.
Formatting rules from USPS Publication 28; reviewed September 2026.
Tell us the full address, unit number included, and we will come back with a starting quote.