The basic format for an apartment address

An apartment address follows the same structure as any street address, with one addition: the unit number. The standard format is: your name, street number and name, apartment or unit number, city, state, and ZIP code — each on its own line when you write it by hand, or separated by commas when you type it in a form.

The apartment number goes on the same line as the street address or on the line directly below it. Both formats work for mail and official documents. The key is that the unit number must be present and clearly marked so mail carriers and delivery services know which door to use.

Here is what a correctly formatted apartment address looks like:

Sarah Martinez 425 Oak Street, Apartment 3B Denver, CO 80202

Or written on a form with commas:

425 Oak Street, Apartment 3B, Denver, CO 80202

Key Takeaways

  • Always include the unit number with a clear label like "Apartment," "Apt," "Unit," or "#" so mail carriers know which door to use.
  • The apartment number can go on the same line as the street address or on the line directly below — both are correct.
  • Use the full ZIP code (five digits) or ZIP+4 code (five digits plus four) if you have it, as this speeds up mail delivery.
  • When filling out online forms, put the apartment number in the field labeled "Apartment," "Unit," or "Suite" rather than combining it with the street address unless the form has no separate field.
  • Double-check your address against your lease or a recent piece of mail to catch typos before submitting it to housing programs or government agencies.

Where the apartment number goes on forms

Most online forms and paper applications have separate fields for street address and unit number. If the form shows a line for "Street Address" and another for "Apartment/Unit/Suite," put the street number and name in the first field and the unit number in the second field. This prevents confusion and ensures your address is processed correctly by computer systems.

If a form has only one address field and no separate unit field, write the full address on one line: "425 Oak Street, Apartment 3B." Do not split it across lines unless the form itself has multiple lines for the address block.

For housing information programs, rental applications, and government forms, using the separate fields correctly matters because the system may reject the address if the unit number is in the wrong place or formatted in a way the computer does not recognize.

How to label your apartment number

Use one of these standard abbreviations or labels before your unit number: "Apartment" (or "Apt"), "Unit," "Suite," or "#". All are correct and widely recognized. The abbreviation "Apt" is the most common on forms and envelopes. "Unit" works for any type of apartment building. "Suite" is often used for commercial spaces but also appears in some residential buildings.

Do not use informal labels like "Apt." with a period followed by a space and then a number written as a word (for example, "Apt. Three B" instead of "Apt. 3B"). Always use numbers for the unit designation, even if the unit is labeled with letters or a combination of numbers and letters.

Examples of correct formats:

  • Apartment 3B or Apt. 3B
  • Unit 12 or Unit 12A
  • Suite 204
  • #5 or #5-C

What to do if your building has no unit number

Some older buildings or small multi-unit properties do not use unit numbers. If your lease or mail does not show a unit number, contact your landlord or property manager to ask what address they use for official purposes. They may have a unit number assigned even if it is not posted on your door.

If the building truly has no unit system, write the address without a unit number and add a clarifying detail if needed — for example, "425 Oak Street, Ground Floor Rear" or "425 Oak Street, Back Building." This helps mail carriers and delivery services find the correct entrance. For housing programs and government forms, call the program directly if the form requires a unit number but your building does not have one; they can note your situation in the process.

Common mistakes to avoid

The most frequent errors are leaving out the unit number entirely, writing it in the wrong place, or abbreviating the city or state. Mail sent to "425 Oak Street, Denver, CO" without the apartment number may go to the building's main office or be returned to the sender. Always include the unit number, even if you think the mail carrier will figure it out.

Do not abbreviate the state name unless you are using the official two-letter postal code (CO for Colorado, CA for California, NY for New York). Do not shorten the city name. Write out the full city name as it appears on your lease or utility bills.

Another common mistake is writing the ZIP code incorrectly. If you know the ZIP+4 code (the nine-digit version), use it — it speeds delivery. If you only know the five-digit ZIP code, that is sufficient. Do not guess or make up digits.

Checking your address against official documents

Before you submit your address to a housing program, rental process, or government agency, compare it to your lease, a recent utility bill, or a piece of mail you received at that address. This catches typos and ensures the address matches what is already on file with the postal service and your landlord.

If your lease shows a different format than what you wrote — for example, if it says "Apt 3-B" but you wrote "Apt. 3B" — use the format from your lease. Consistency matters when programs are verifying your residency or sending documents to you.

If you have moved recently and are not sure which address to use, use your current address where you actually live. Housing programs need to reach you at the place where you reside now, not a previous address.

Frequently Asked Questions

Should I write "Apartment" or "Apt" on official documents?

Both are correct and equally accepted. "Apartment" is the full word; "Apt" is the standard abbreviation. Use whichever matches the format on your lease or the form you are filling out. For consistency, match what your landlord or utility company uses.

What if my apartment has a letter instead of a number, like 3B?

Write it exactly as it appears on your lease and mailbox: "Apartment 3B" or "Apt. 3B." Do not spell out the letter. If your unit is labeled "3-B" with a hyphen, use the hyphen. Matching the exact format prevents mail from being misdelivered.

Do I need to include the apartment number if I am mailing something to myself?

Yes. Always include the unit number on any address, whether you are mailing to yourself or someone else. Mail carriers use the unit number to deliver to the correct door. Without it, mail may be delayed or delivered to the wrong unit.

What goes in the address field if my building uses suite numbers instead of apartment numbers?

Write it the same way: "425 Oak Street, Suite 3B" or "Suite 3B" in the unit field if the form has a separate one. Suite numbers work identically to apartment numbers for mailing and form purposes.

Can I use a PO box instead of my apartment address for housing programs?

No. Housing programs, rental applications, and government agencies require your actual residential address — the physical location where you live. A PO box is not a residential address and will not work for these purposes. Always provide your apartment address.