The correct format puts the apartment number on the same line as the street address
When you type an address that includes an apartment, unit, or suite number, put that number on the same line as the street address, separated by a comma. The format is: street number and name, then apartment/unit/suite identifier, then city, state, and ZIP code all on separate lines.
Most online forms and mailing systems expect this layout because it matches how the postal service sorts mail. If you put the apartment number on a separate line or in the wrong spot, your package may arrive at the building but get stuck in the mail room, or an online order might fail to process because the system doesn't recognize the address.
The reason this matters: address databases used by shipping companies, banks, and government agencies all parse addresses the same way. When you follow the standard format, your information goes into the right fields automatically. When you don't, a human has to fix it later — or it doesn't get fixed at all.
Key Takeaways
- Write the apartment number on the same line as the street address, separated by a comma: "123 Main Street, Apt 4B".
- The order from top to bottom is: street address with apartment, city, state, ZIP code — never put apartment information below the city.
- Use "Apt", "Unit", "Suite", or "#" before the number; all are recognized by postal and shipping systems.
- If an online form has separate fields for "Street Address" and "Apartment/Unit", use those fields instead of typing it all in one line.
The standard format for a mailing address
The United States Postal Service (USPS) recognizes this layout as the official standard:
| Line 1 | Street number, street name, apartment/unit number |
| Line 2 | City, state, ZIP code |
An actual example would look like this:
456 Oak Avenue, Unit 12 Portland, OR 97201
The apartment identifier comes after a comma and a space. You can use "Apt", "Unit", "Suite", "#", or "Ste" — the postal service understands all of them. The number itself can be numeric (Apt 5), alphanumeric (Apt 5B), or a suite name (Suite 200). What matters is that it stays on the same line as the street address.
What to do when a form has separate address fields
Many websites split the address into multiple input boxes: one for "Street Address", another for "Apartment/Unit", and a third for "City". When you see this layout, use each field for its intended purpose instead of trying to fit everything into the first box.
Type the street number and name in the first field — "456 Oak Avenue" — and the apartment identifier in the second field — "Unit 12". This way the system stores each piece of information correctly. If you type "456 Oak Avenue, Unit 12" in the street field and leave the apartment field blank, some systems will reject it or misread it.
If the form only has one address field and no separate apartment box, then use the comma format: "456 Oak Avenue, Unit 12". The system will accept it because it matches the postal standard.
Common mistakes that cause delivery or processing problems
Putting the apartment number on a second line by itself is the most frequent error. A form that shows two lines might tempt you to type the street address on line one and "Apt 5" on line two. Shipping and address-verification systems read this as two separate addresses and often reject it or send your package to the building's main entrance instead of your unit.
Another mistake is using a slash or dash without a space: "456 Oak Avenue/5" or "456 Oak Avenue-5". While humans can read these, automated systems sometimes fail to parse them correctly. Stick to a comma and space: "456 Oak Avenue, Apt 5".
Abbreviating the street type inconsistently also causes problems. If the postal database has "Avenue" spelled out but you type "Ave", the system might not match the address. Use the full spelling when you know it, or match whatever appears on your lease or official mail.
How to format an address when you don't have an apartment number
If your building has no apartment numbers — common in small houses or older buildings — type only the street address and city information. Do not invent an apartment number or add "No Apt" or "N/A". The postal service and shipping systems handle buildings without unit numbers correctly when you straightforward omit that information.
If you live in a house with a name instead of a number — "The Willows" or "Riverside Farm" — type the property name on the first line where the street address would go, then the street address on the second line. This is less common but the postal service recognizes it.
International addresses and special cases
If you are shipping to a country outside the United States, the apartment format may differ. Canada uses "Apt" or "Unit" the same way, but the United Kingdom often uses "Flat" instead. Check the destination country's postal guidelines if you are unsure.
For a PO Box, do not include an apartment number. Type only the PO Box number and city information. A PO Box is already a unique address; adding apartment information will confuse the system.
If you are filling out a form for a business address and the business occupies multiple suites in one building, the suite number follows the same comma format: "789 Commerce Drive, Suite 300".
Testing your address before you submit
Before you place an order or submit a form, read the address back to yourself in the format you typed it. Does the apartment number appear on the same line as the street address, separated by a comma? Is the city, state, and ZIP code on a separate line below? If yes, you are formatted correctly.
If the website has an address verification tool — many shipping and banking sites do — use it. Type your address and the system will show you how it parsed each part. If the apartment number appears in the wrong field or is missing, you will see it when ready and can correct it before submitting.
Frequently Asked Questions
Should I put "Apartment" or just "Apt"?
Either works. "Apt" is shorter and more common in online forms, but "Apartment" spelled out is equally valid. The postal service and shipping systems recognize both. Use whichever fits the space available or matches the style of your lease.
What if my apartment has a letter instead of a number, like 5B?
Type it exactly as it appears on your lease or mailbox: "456 Oak Avenue, Apt 5B". The letter is part of your address identifier and must be included so mail reaches the correct unit.
Can I type the apartment number in parentheses instead of after a comma?
Avoid it. Parentheses can confuse automated address systems. Stick to the comma format: "456 Oak Avenue, Apt 5" rather than "456 Oak Avenue (Apt 5)". The comma is what postal and shipping databases expect.
What happens if I forget to include the apartment number?
Your package or mail will arrive at the building's main address but may not reach your specific unit. It could sit in a lobby mailroom or be returned to the sender. Always include the apartment number if your building has one.
Do I need to include the apartment number when writing an address by hand on an envelope?
Yes. Write it the same way: street address and apartment number on the first line, city and state on the second line. The postal carrier needs the apartment number to deliver to the correct unit.