The Correct Way to Write an Apartment Address in the U.S

Whether you're filling out a rental application, updating your billing information, or sending a package, writing an apartment address correctly ensures that what you send—or receive—gets to the right place. Improperly written addresses are among the most common causes of lost mail and delivery delays in the U.S.

For renters and property owners alike—especially those moving in or out through HeroSold’s home selling services—knowing how to format an apartment address is an essential skill. This guide breaks down the official USPS formatting rules, common mistakes, best practices, and how to adapt the structure for unique housing situations.

1. Basic Format for Writing a U.S. Apartment Address

The United States Postal Service (USPS) has a standardized three-line format for mailing addresses:

Full Name:

Street Address + Apartment Number:

City, State ZIP+4 Code:

Example:

JANE DOE

123 MAIN ST APT 4B

SPRINGFIELD, IL 62704-3056

This format ensures mail is sorted efficiently through automation and is deliverable with minimal delay.

2. Where to Place the Apartment Number

The apartment number should be placed on the second line, directly after the street address. There are a few acceptable variations depending on spacing and context:

123 Maple Ave APT 3C

123 Maple Ave #3C

123 Maple Ave UNIT 3C

While all are technically correct, "APT" and "UNIT" are preferred in more formal or government-related documents. Avoid splitting the apartment number onto a new line unless space limits require it.

3. Accepted Abbreviations and Capitalization Guidelines

The USPS recommends using ALL CAPS and official abbreviations to improve clarity and automation accuracy. Here's a quick reference of commonly used abbreviations:

Term Abbreviation: 

Apartment : APT

Unit: UNIT

Suite: STE

Building: BLDG

Street: ST

Road: RD

Avenue: AVE

Boulevard: BLVD

Example:

MARK RIVERS

789 OAK BLVD UNIT 22B

DENVER, CO 80203

Tips:

Don’t use periods (e.g., ST. or APT.)

Avoid using lowercase or camel case formatting (e.g., “123 Oak St. Apt. 5b”)

4. Common Mistakes and How to Avoid Them

Incorrectly formatted addresses can delay deliveries or result in mail being returned. Here are frequent errors and ways to fix them:

Missing Apartment Number: Always include the unit number; otherwise, the delivery might fail.

Line Break Errors: Putting the apartment number on a separate line (e.g., Line 3) can cause confusion unless absolutely necessary.

Unrecognized Abbreviations: Stick with USPS-approved abbreviations like "APT" and avoid variations like "Apart#".

Poor Legibility: Always write in block letters if handwritten. Use black or blue ink for contrast.

Bad Example:

Jane D.

123 oak street

apartment #4B

springfield, illinois 62704

Corrected Version:

JANE D

123 OAK ST APT 4B

SPRINGFIELD, IL 62704

5. ZIP+4 Code: Is It Necessary?

The ZIP+4 code includes the basic five-digit ZIP plus an extra four digits that help USPS route mail even faster. It’s not mandatory, but using it can:

Reduce delivery errors

Speed up sorting

Improve chances of on-time delivery

To find your ZIP+4 code, use the USPS ZIP Code Lookup Tool.

Example:

LISA TRAN

2500 BROADWAY ST APT 14C

NEW YORK, NY 10025-7513

6. Special Cases: Multi-Building or Gated Communities

If your apartment complex has multiple buildings or entrances, you may need to include extra details:

With Building Number:

CARLOS SANCHEZ

500 RIVER RD BLDG 3 APT 201

DALLAS, TX 75201

With PO Box and Unit:

TINA CHEN

PO BOX 1426 UNIT 7B

PHOENIX, AZ 85001

When using third-party platforms, confirm how they want addresses input to avoid truncation or mismatches.

7. Best Practices for Addressing Envelopes and Forms

To ensure success when writing or printing apartment addresses:

• Always include your full legal name to match mailbox records or ID.

• Use block lettering when writing by hand.

• Avoid extra punctuation unless formatting requires it.

• Left-align text for easier machine reading.

• Double-check spelling of city and verify ZIP code.

• Include a return address in the top-left corner.

Whether you're updating legal documents, applying for loans, or shipping items, sticking to these practices increases the chance of accurate, timely delivery.

If you're planning to move soon, check out HeroSold’s quick-sale process to ensure a smooth transition. You can also sell your home faster by working with a trusted team and getting a free home evaluation. When in doubt, call a professional real estate agent to guide you through the selling process.

8. Apartment Addressing FAQs

Q: Can I use # instead of APT?

A: Yes, but make sure it’s followed by a space. “#4B” is acceptable, but “APT 4B” is more formal and preferred for official use.

Q: Is it okay to leave out the apartment number?

A: No. Leaving out the apartment number is one of the most common causes of returned or misdelivered mail.

Q: Does capitalization matter?

A: It’s not required, but using ALL CAPS improves legibility and reduces processing errors.

Q: Should I include commas in the address?

A: USPS guidelines suggest omitting commas within address lines.

Conclusion: Simple Formatting for Reliable Delivery

Writing your apartment address the right way might seem minor—but it has major implications for mail delivery, service setup, and legal documentation. Following USPS formatting ensures that your correspondence, packages, and important documents reach you on time.

If you're planning a move or updating your contact details as part of a property sale or rental process, using a trusted platform like HeroSold can simplify the transition. Just don’t forget to double-check your address before hitting submit.