Write the apartment number on the same line as the street address
The apartment number goes on the same line as your street address, after the street name. Use either "Apt." or "#" followed by the number, with a space between the street address and the apartment designation. For example: 123 Main Street Apt. 4B or 123 Main Street #4B.
Both formats are accepted by the U.S. Postal Service and will reach your mailbox. The "Apt." format is more formal and commonly used on official documents, while "#" is shorter and increasingly common on informal mail and online forms. Pick one and use it consistently on your lease, bills, and mail forwarding requests so mail carriers and delivery services recognize your address the same way each time.
Never put the apartment number on a separate line or in a different position. Mail sorting machines read addresses line by line in a specific order, and moving the apartment number confuses the system. Your mail may be delayed or delivered to the wrong unit if the format is wrong.
Key Takeaways
- The apartment number belongs on the same line as the street address, after the street name, using either "Apt." or "#".
- Both "Apt. 4B" and "#4B" are correct formats and will be delivered, but use the same format consistently across all documents.
- Never split the street address and apartment number onto separate lines, as mail sorting machines may misread it.
- When filling out online forms, use the format the form requests — some have separate fields for street address and apartment number.
- Your lease, utility bills, and mail forwarding request should all show your address in the same format to prevent delivery delays.
What to do when a form has separate fields for street and apartment
Many online forms, rental applications, and government websites have two separate boxes: one for "Street Address" and one for "Apt/Unit Number" or "Apartment." When this happens, put only the street address in the first box and the apartment number in the second box. Do not repeat the street address in the apartment field.
This separation is intentional — the form is designed to organize the information for a database or mailing system. Filling it correctly means your address will be stored and printed the right way on the other end. If you put "123 Main Street Apt. 4B" in the street field and leave the apartment field blank, the system may not recognize that you live in an apartment at all.
Formatting for mail and packages
When writing an address by hand on an envelope or package, follow this order from top to bottom:
- Recipient's name
- Street address with apartment number (same line)
- City, state, and ZIP code
Example:
Sarah Chen 456 Oak Avenue Apt. 12 Portland, OR 97201
Leave space between each line so the address is straightforward to read. Write clearly in blue or black ink. The U.S. Postal Service prefers addresses in all capital letters on official mail, but lowercase is fine for personal correspondence and will still be delivered.
Common apartment number formats
Apartment numbers come in different styles depending on how your building is organized. Single-digit numbers (Apt. 1, Apt. 2) are common in smaller buildings. Multi-digit numbers with letters (Apt. 4B, Apt. 12C) usually mean the building has multiple floors or sections — the number is the unit and the letter indicates the floor or wing. Some buildings use only letters (Apt. A, Apt. B) or a combination like 3-D (unit 3, section D).
Write your apartment number exactly as it appears on your lease and mailbox. If your lease says "Unit 4B," use "Unit 4B" or "Apt. 4B" — both are correct, but consistency matters more than which one you choose. If you are unsure of the exact format, check your lease, look at your mailbox, or ask your landlord or property manager.
What happens if you write the address wrong
Mail written with the apartment number on a separate line or in the wrong position may be delayed by one to three days while postal workers sort it manually. In some cases, mail carriers know the building well enough to deliver it anyway. In others — especially in large apartment complexes or unfamiliar areas — your mail may be returned to the sender or held at the post office.
Packages from delivery services like UPS, FedEx, and Amazon are more sensitive to address format than regular mail. A missing or incorrectly placed apartment number can cause a package to be left at the wrong unit, returned to the sender, or held for pickup. This is why using the same address format on your online shopping accounts, delivery instructions, and mail forwarding request is important.
Setting up mail forwarding with the correct address
When you move into an apartment, the address you submit for mail forwarding should match the format on your lease. Go to USPS.com or visit your local post office to file a change of address form. Write your new apartment address exactly as you plan to use it going forward — apartment number on the same line as the street address.
If you are moving from one apartment to another, update your address with your employer, bank, insurance company, and any subscription services before you move. This prevents mail from being forwarded twice and reduces the chance of delays. The post office forwards mail for up to 12 months, but it is faster and more reliable to update your address directly with each sender.
Frequently Asked Questions
Should I use "Apt." or "#" for my apartment number?
Both are correct and accepted by the postal service. "Apt." is more formal and commonly used on official documents and leases. "#" is shorter and increasingly common on informal mail and online forms. Choose one and use it consistently across all your documents — consistency matters more than which format you pick.
What if my apartment doesn't have a number, only a letter?
Write it the same way: street address, then the letter. For example, "789 Pine Road Apt. A" or "789 Pine Road #A." If your lease or mailbox shows a different format, match that exactly.
Can I put the apartment number on the second line instead of the first?
You can, but it is not recommended. Mail sorting machines read addresses line by line in order, and moving the apartment number to a separate line may confuse the system. Your mail may be delayed or delivered to the wrong unit. Keep the apartment number on the same line as the street address for the fastest, most reliable delivery.
Do I need to include "Apt." if the form already says "Apartment Number"?
No. If the form has a separate field labeled "Apartment Number" or "Unit Number," put only the number or letter in that field — just "4B," not "Apt. 4B." The form already knows it is an apartment number, so repeating "Apt." creates a duplicate.
What if I do not know my apartment number format?
Check your lease, look at your mailbox, or ask your landlord or property manager. Using the exact format from your lease ensures your address is recognized consistently by mail carriers, delivery services, and government agencies.