To write an address with an apartment number in the United States, place the apartment number after the street address on the same line, using the abbreviation APT. For example, the correct USPS-preferred format is:
JANE DOE 123 MAIN ST APT 4B ANYTOWN NY 12345
This is a fictional address used to demonstrate the format. The apartment number identifies the specific unit within a building and helps ensure that letters and packages reach the correct recipient.
How to Write an Address With an Apartment Number
According to the United States Postal Service (USPS), an apartment address should contain the recipient’s name, street address, apartment designation, city, state, and ZIP Code.
Follow this order when writing an apartment address:
- Recipient’s full name. Write the name of the person receiving the mail on the first line.
- Street number and name. Include the building number and street name, using standard abbreviations when appropriate.
- Apartment number. Add APT followed by the apartment number or letter combination.
- City, state, and ZIP Code. Write these on the last line, using the official two-letter state abbreviation.
Preferred USPS format — apartment number on the same line:
JANE DOE 123 MAIN ST APT 4B ANYTOWN NY 12345
Alternative format — apartment number on a separate line:
JANE DOE APT 4B 123 MAIN ST ANYTOWN NY 12345
USPS recommends placing the apartment number at the end of the street address line. If there is not enough space, put the apartment information on the line immediately above the street address, not below it.
For mailed letters and packages, USPS also recommends uppercase letters, standard abbreviations, and minimal punctuation to improve readability and automated processing.
These guidelines are explained in USPS Publication 28, Section 213.
What Does Apt Mean in an Address?
APT is the standard USPS abbreviation for apartment. It identifies a specific residential unit within a building containing multiple apartments.
The abbreviation is followed by the apartment’s number or alphanumeric designation. Common examples include:
- APT 5 — Apartment 5.
- APT 12B — Apartment 12B.
- APT 203 — Apartment 203.
In everyday writing, people sometimes use “Apt.” with a period. However, official USPS formatting uses APT without punctuation.
Other common secondary address abbreviations include:
| Abbreviation | Meaning |
|---|---|
| APT | Apartment |
| STE | Suite |
| UNIT | Unit |
| BLDG | Building |
| FL | Floor |
These terms are not always interchangeable. For example, STE commonly identifies a suite, while APT specifically refers to an apartment. Use the designation that matches the actual mailing address.
Where Do You Put the Apartment Number in an Online Address Form?
Online shopping sites, delivery services, and registration forms often separate addresses into multiple fields. In these cases, the apartment number usually belongs in Address Line 2.
Example of a completed online address form:
| Field | Example |
|---|---|
| Address Line 1 | 123 Main St |
| Address Line 2 | Apt 4B |
| City | Anytown |
| State | NY |
| ZIP Code | 12345 |
Address Line 1 normally contains the street number and street name. Address Line 2 is used for additional delivery information, such as an apartment, suite, or unit number.
If a website does not provide Address Line 2, enter the apartment number after the street address in Address Line 1. For example: 123 Main St Apt 4B.
Some online forms have a dedicated apartment or unit number field. When available, use that field instead. The arrangement of online form fields does not have to match the final printed mailing address exactly.
Can You Use # Instead of Apt in an Address?
The pound sign (#) is sometimes used to identify an apartment or another unit within a building. However, USPS recommends using the specific designation, such as APT, when it is known.
Address using the pound sign:
123 MAIN ST # 4B
Preferred apartment address:
123 MAIN ST APT 4B
If you use #, USPS requires a space between the symbol and the unit number. Writing APT is generally clearer because it explicitly identifies the unit as an apartment.
Common Mistakes When Writing Apartment Addresses
Even small address formatting errors can cause delivery delays or make a package difficult to locate.
- Leaving out the apartment number. Without it, the delivery carrier may not know which unit should receive the mail.
- Putting the apartment number after the ZIP Code. Apartment information belongs with the street address, not after the city, state, or ZIP Code.
- Using the wrong unit designation. Avoid replacing APT with STE or UNIT unless that designation matches the actual address.
- Entering an incorrect ZIP Code or state abbreviation. Verify the five-digit ZIP Code and use the correct two-letter state abbreviation.
If you are unsure about the correct mailing address, use the official USPS ZIP Code Lookup tool to verify the standardized address and ZIP Code.
In summary, the easiest way to write an apartment address is to place APT and the apartment number immediately after the street name. On envelopes, keep this information on the same line whenever possible. In online forms, use Address Line 2 or the dedicated apartment field to ensure accurate delivery.
