Write the apartment number after the street address on the same line, separated by a comma or the abbreviation "Apt."

The standard format is: street number and name, Apt. [number], city, state, ZIP code. For example: 425 Oak Street, Apt. 12B, Denver, CO 80202. The apartment number comes after the street address but before the city. You can use "Apt." or "Apartment" — both are correct, though "Apt." is more common in mail sorting.

The U.S. Postal Service (USPS) accepts both formats equally. What matters most is that the apartment number is present and clearly legible. Mail carriers use it to distinguish your unit from others at the same street address, so leaving it out or placing it in the wrong spot can delay delivery or send mail to the wrong door.

Key Takeaways

  • Place the apartment number on the same line as the street address, after the street name and separated by a comma or "Apt."
  • The correct order is street address, apartment number, city, state, ZIP code — all on separate lines or formatted as one continuous address.
  • Use "Apt." or "Apartment" — the USPS recognizes both, and either works for mail delivery.
  • If your apartment has a letter (like 12B), include it exactly as shown on your lease or building directory.

The two standard formats USPS accepts

Most mail carriers see addresses formatted one of two ways. The first puts everything on separate lines:

425 Oak Street Apt. 12B Denver, CO 80202

The second keeps the street address and apartment number on the same line, separated by a comma:

425 Oak Street, Apt. 12B Denver, CO 80202

Both formats work equally well. The USPS processes mail the same way regardless of which you use. The key is that the apartment number appears somewhere on the address label, is straightforward to read, and matches what the building uses internally.

When your apartment has a letter or unusual format

Some buildings use letters instead of numbers (Apt. A, Apt. B), numbers with letters (12B, 3C), or combinations like "Unit 205-West" or "Suite 150." Write it exactly as it appears on your lease, your mailbox, or the building directory. The mail carrier needs to match what you write to what is posted at the building.

If you are unsure of the exact format, check your lease, your mailbox label, or ask the building manager. Inconsistency between what you write and what the building uses is the most common reason mail gets delayed or delivered to the wrong unit. Once you confirm the format, use it the same way every time.

Where NOT to put the apartment number

Do not put the apartment number on a separate line below the city and state. The USPS reads addresses top to bottom, and placing it at the bottom can cause the mail sorting machine to misread or skip it. Do not abbreviate the apartment number as just "#" — write out "Apt." or "Apartment" or "Unit" so it is clear.

Avoid putting the apartment number in parentheses or brackets, like "425 Oak Street (Apt. 12B)." While some mail carriers will still deliver it correctly, the USPS scanning equipment reads these formats less reliably. Stick to the standard comma or "Apt." separator.

Apartment numbers on shipping labels and online forms

When filling out an online order form or shipping label, look for a field labeled "Apartment," "Unit," "Suite," or "Address Line 2." Enter your apartment number there, not in the main street address field. If there is no separate field, add it to the end of the street address line with a comma, like "425 Oak Street, Apt. 12B."

Some retailers and shipping companies have strict formatting rules. If the form rejects your entry, try removing punctuation or abbreviating differently — for example, "Apt 12B" instead of "Apt. 12B" — but this is rare. Most systems accept standard formats without complaint.

Handwriting your address on mail or packages

Write clearly and in black or blue ink. Make sure the apartment number is as large and legible as the street address. If you are writing on a small label or envelope, you may need to abbreviate — "Apt." instead of "Apartment" — but never skip the number itself.

Leave space between the street address and apartment number so they do not run together. A mail carrier reading your handwriting should be able to see at a glance that there is a street address, an apartment number, and a city/state/ZIP. If your handwriting is hard to read, consider printing or using a label maker instead.

Frequently Asked Questions

Can I use "Unit" instead of "Apt."?

Yes. "Unit," "Apt.," "Apartment," and "Suite" are all recognized by the USPS. Use whichever term your building uses on its directory or your lease. Consistency matters more than which abbreviation you choose.

What if I do not know my apartment number?

Check your lease, your mailbox label, or the building directory near the entrance. If none of those show it, ask the building manager or landlord. Your apartment number is assigned by the building, not by you, so it should be documented somewhere official.

Does the apartment number go before or after the city?

The apartment number always goes before the city. The order is: street address, apartment number, city, state, ZIP code. Putting the apartment number after the city confuses mail sorting machines and can delay delivery.

What if my building uses both a number and a letter, like "12B"?

Write it exactly as shown — "Apt. 12B" or "Unit 12B." Do not separate the number and letter or rearrange them. The building's internal system uses that exact format to route mail to the right mailbox.

Will mail still arrive if I forget the apartment number?

Sometimes, but not reliably. If the building is small or the mail carrier knows the residents, it may arrive anyway. In larger buildings, mail without an apartment number often gets returned to the sender or held at the post office. Always include it to avoid delays.