Write the apartment number on the same line as the street address

The apartment number goes on the same line as the street address, after the street name. Use either "Apt." or "#" followed by the unit number. Both formats work equally well with mail carriers. For example: 425 Oak Street Apt. 12 or 425 Oak Street #12.

Do not put the apartment number on a separate line by itself. Mail sorting machines read addresses line by line, and an apartment number alone on its own line can cause delays or misrouting. The machine needs to see the street address and unit together to match it to the correct delivery point.

Key Takeaways

  • Write the apartment number on the same line as the street address, after the street name, using either "Apt." or "#".
  • Never put the apartment number on a separate line or in a different position — mail sorting machines need the full address together.
  • Use the exact apartment number format shown on your lease or building directory, even if it includes letters or unusual numbering.
  • The recipient's name goes on the first line, the full street address with apartment on the second line, and the city, state, and ZIP code on the third line.

The standard three-line format for apartment mail

A properly addressed envelope follows a three-line format. The first line is the recipient's name. The second line is the street address with the apartment number. The third line is the city, state, and ZIP code.

Here is what it looks like in practice:

Sarah Johnson 425 Oak Street Apt. 12 Portland, OR 97214

This layout works for all mail carriers and sorting systems. The spacing and line breaks matter because automated machines scan from top to bottom and left to right. Keeping the address components in the expected positions reduces the chance of a delay.

When your apartment uses letters or non-standard numbering

Some buildings use letters, dashes, or other formats for unit numbers — for example, Apt. 12-B, Apt. 201C, or Unit 3A. Write the apartment designation exactly as it appears on your lease, your building directory, or your mailbox. Do not simplify or rearrange it.

If you are unsure of the exact format, check your lease, ask your landlord or building management, or look at how it is printed on your mailbox. Using the correct format prevents mail from being delivered to the wrong unit, especially in large buildings where similar numbers might exist.

Placement on the envelope itself

Write the address in the center of the envelope, starting about one inch from the top and leaving space on all sides. Use a pen or permanent marker so the address does not smudge or fade. The address should be straightforward to read — use print rather than cursive if possible, and keep letters and numbers at a consistent size.

The return address (your name and address) goes in the upper left corner of the envelope. This tells the postal service where to send the mail if it cannot be delivered. If you are sending mail from an apartment, include your apartment number in the return address as well.

Common mistakes that delay apartment mail

The most common error is putting the apartment number on a separate line below the street address. This confuses sorting machines and can cause the mail to be sent to the building's main address instead of your specific unit. Another frequent mistake is using an incorrect or incomplete apartment number — for example, writing "Apt. 2" when the actual unit is "Apt. 2B".

Illegible handwriting is also a problem. If a mail carrier cannot read the apartment number clearly, they may leave the mail at the building entrance or return it to the sender. Take time to write the address neatly, and if you are addressing many envelopes, consider typing and printing the addresses instead.

What to do if your building has a mailroom or central mail location

Some apartment buildings have a mailroom or central mail area where all residents' mail is sorted and distributed. In these buildings, you can still address mail to your apartment number — the building's mail staff will sort it to your box or slot. You do not need to use a different address format.

If your building uses a mailroom, the postal carrier delivers all mail to that location, and building staff handle the final delivery to individual units. Your apartment number on the envelope ensures the mail reaches your box, not someone else's.

Frequently Asked Questions

Should I write "Apartment" or "Apt." or use the "#" symbol?

All three formats work: "Apartment 12," "Apt. 12," and "#12" are equally acceptable to mail carriers. Use whichever you prefer or whichever matches the format on your lease. Consistency helps, but the postal service recognizes all three.

What if I do not know my exact apartment number?

Check your lease, your mailbox, your building directory, or ask your landlord or building management. Using the wrong number can send mail to a neighbor's unit. If you are receiving mail at the building and it keeps going to the wrong place, contact your local post office — they can help you confirm the correct address format for your unit.

Can I write the apartment number in parentheses or brackets?

It is better to avoid parentheses and brackets. Stick with the standard formats: "Apt. 12" or "#12". Unusual punctuation can confuse sorting machines or be misread by hand. The standard formats are fastest and most reliable.

Does the ZIP code change if I live in an apartment?

No. Your ZIP code is the same whether you live in a house or an apartment. The apartment number is additional information that directs the mail to your specific unit within that ZIP code area.