The standard abbreviation for apartment is "apt" or "Apt."
When you see a mailing address or rental listing, "apt" is the shorthand you'll encounter most often. It appears after the street address and before the unit number — for example, "123 Main Street, Apt. 4B" or "456 Oak Avenue, apt. 12." Both lowercase and capitalized versions are correct, though capitalized is more common in formal addresses.
Real estate listings, lease documents, and postal mail all use this abbreviation. The U.S. Postal Service recognizes it, so using "apt" on an envelope or package label will reach the right unit without delay. You may also see it written out fully as "apartment," particularly in formal documents like purchase agreements or official correspondence, but "apt" is the standard shorthand across the industry.
Key Takeaways
- The abbreviation "apt" or "Apt." is used in addresses to identify which unit number within a building you live in or are mailing to.
- Both capitalized and lowercase versions are acceptable, though capitalized is more formal and common in official addresses.
- The U.S. Postal Service recognizes "apt" as a standard abbreviation, so mail addressed this way will be delivered correctly.
- You may also encounter "unit" used interchangeably with "apt" in some regions or on certain rental platforms.
- Always include the apartment number when writing your address to may support mail and deliveries reach the correct location.
Where you'll see "apt" used
Rental listings almost always use "apt" to describe the property type and to show unit numbers. When you search for apartments online, the listing title might say "2BR apt" to mean a two-bedroom apartment. The address section will then show the specific unit as "apt. 301" or similar.
Lease agreements and rental applications use the full word "apartment" in the body text but abbreviate it to "apt" in the address block at the top. Government forms, tax documents, and utility bills all follow the same pattern — the abbreviation appears in the address line, not in the descriptive text.
Other abbreviations you might see
Some regions and platforms use "unit" instead of "apt" — you'll see this especially in newer buildings or in areas where "unit" is the local convention. "Unit 4" and "Apt. 4" mean the same thing and are both correct. A few older documents or regional styles may use "no." (number) followed by the unit number, as in "123 Main Street, No. 5," but this is less common today.
On some rental websites, you may see abbreviations like "BR" for bedroom (as in "2BR apt") or "BA" for bathroom. These are informal shorthand used in listing titles to save space, not official postal abbreviations.
How to write your address correctly
The standard format is street address, then apartment number, then city, state, and ZIP code. The apartment line can be written as "Apt. 4B," "apt 4B," or "Unit 4B" — all are correct. The USPS prefers the apartment number on the same line as the street address when possible, formatted as "123 Main Street Apt. 4B" or on a separate line directly below the street address.
If you're filling out a form with separate fields for street address and apartment number, put the street address in the first field and the apartment number (with or without "apt") in the second. When writing by hand on an envelope, putting the apartment number on the line below the street address is clearest and most reliable for mail carriers.
Why the abbreviation matters for mail delivery
Mail carriers use the apartment number to sort packages and letters to the correct unit. Without it, mail may be delivered to the building's main office or held until someone can determine which unit it belongs to. This can delay delivery by days, especially for packages or time-sensitive documents.
When you move into an apartment, confirm your official unit number with your landlord or property manager — sometimes it's written differently on different documents. Use that exact number consistently on all addresses: mail, online accounts, delivery services, and official forms. This prevents mail from being misdelivered to a neighboring unit or returned to the sender.
Abbreviations on lease documents and legal paperwork
Lease agreements typically write out "apartment" in full when describing the property itself ("the apartment located at..."), but abbreviate it as "apt" in the address block. The same applies to purchase agreements if you're buying a condo unit. Insurance documents, tax forms, and utility bills follow this pattern — formal language in the body, abbreviations in the address section.
If you're signing documents or filling out forms, you don't need to worry about which version to use; the form will have a specific field or line for the apartment number, and you can write it however is clearest. Official records will standardize it on their end.
Frequently Asked Questions
Is "apt" the only correct abbreviation for apartment?
"Apt" is the standard abbreviation recognized by the U.S. Postal Service and used across the real estate industry. "Unit" is also widely accepted and means the same thing. Both will work on addresses and mail. Other abbreviations like "no." are less common but may appear in older documents.
Should I capitalize "apt" or leave it lowercase?
Both are correct. Capitalized "Apt." is more formal and common in official addresses and formal documents. Lowercase "apt" is acceptable and often used in casual writing, online listings, and informal contexts. Choose whichever matches the style of the document you're filling out.
What if my apartment doesn't have a number, just a letter?
Write it the same way: "Apt. A" or "Apt. 1A" depending on how your unit is labeled. Use whatever designation appears on your lease or mailbox. Mail carriers are familiar with letter-only and mixed letter-number units and will deliver correctly as long as the designation is clear.
Can I write my address without the "apt" abbreviation?
You can write it out as "apartment" instead, and mail will still be delivered. However, using the standard abbreviation "apt" is clearer and faster for postal workers to process. For consistency and to avoid delays, use "apt" or "unit" on all addresses, especially packages and time-sensitive mail.
Do online retailers and delivery services recognize "apt" abbreviations?
Yes. Amazon, UPS, FedEx, and other delivery services all recognize "apt" and "unit" as standard abbreviations. Enter your apartment number in the address field however the form allows — most will accept "Apt. 4B," "apt 4B," or "Unit 4B" without issue. If the form has a separate field for apartment number, use that field.