Put your apartment number after the street address on the same line, or on a separate line directly below it

The two standard formats both work with the postal service and with most online forms. The first puts everything on one line: 123 Main Street, Apt 4B, City, State 12345. The second breaks it into two lines: 123 Main Street / Apt 4B / City, State 12345. Either way, the apartment number comes after the street address, never before it.

The format matters most when you are filling out a form with separate fields. If a form has a line for "Street Address" and another for "Apartment/Unit Number", put only the street address in the first field and only the apartment number in the second. Do not repeat the street address or add extra words like "Unit" or "Suite" unless the form specifically asks for them.

Some forms have only one address field. In that case, use the single-line format: street address, then apartment number, then city and state. This is what mail carriers and delivery services expect to see, and it is what online systems are built to parse.

Key Takeaways

  • Apartment numbers go after the street address, either on the same line separated by a comma or on the line directly below.
  • Use "Apt" or "Apt." before the number, or use "Unit" or "#" — all are accepted by the postal service.
  • When a form has separate fields for street address and apartment number, fill each field with only what it asks for.
  • Never put the apartment number before the street address, and never leave it off if you have one.
  • If you are unsure which format a website or form expects, the single-line format with a comma works almost everywhere.

What abbreviations the postal service accepts

The U.S. Postal Service recognizes several ways to write an apartment number. Apt and Apt. are the most common. Unit, Ste (for suite), and # (the number symbol alone) all work. You do not have to use any abbreviation at all — writing out "Apartment 4B" is correct, though it takes more space.

Consistency matters more than which abbreviation you choose. If you use "Apt 4B" on one document, use "Apt 4B" on all of them. Switching between "Apt", "Unit", and "#" can slow down mail delivery or cause online forms to reject your address as inconsistent with what is on file.

How to format apartment numbers in online forms and applications

Most housing, rental, and government forms have two separate fields: one for street address and one for apartment or unit number. Put only the street address (123 Main Street) in the first field. Put only the apartment identifier (4B, Apt 4B, or Unit 4B) in the second field, depending on what the form asks for.

If a form has only one address field and you have an apartment number, write it as: 123 Main Street, Apt 4B, City, State 12345. Do not add extra punctuation or words. Some online systems are sensitive to commas or extra spaces and may reject the address or flag it for manual review.

When filling out rental applications, lease agreements, or housing authority forms, match the format used in your lease or the format your landlord gave you. If your lease says "Unit 4B", use "Unit 4B" everywhere. If it says "Apt 4B", use that instead. Mismatches between documents can delay processing or cause mail to be returned.

Apartment numbers and mail delivery

Mail carriers use the apartment number to sort mail to the right unit. If you leave it off, your mail may go to the building's main office or to a neighbor's unit. If you write it in the wrong place (before the street address, for example), the postal service may still deliver it, but it will take longer.

When you move into an apartment, confirm the exact format your building uses. Some buildings use "Apt 4B", others use "Unit 4B", and some use only the number "4B". Ask your landlord or the building manager what format appears on the mailbox or lease. Use that same format when you update your address with banks, employers, insurance companies, and government agencies.

What to do if a form does not have a separate apartment field

Some older websites, government forms, or paper applications have only one line for your full address. When that happens, write the street address and apartment number together on that one line, separated by a comma: 123 Main Street, Apt 4B, City, State 12345. This format is recognized by the postal service and by most address-matching systems.

If the form is online and rejects your address, try removing punctuation: 123 Main Street Apt 4B City State 12345. If that does not work, contact the organization directly and ask how they want apartment numbers formatted. Some government agencies and older systems have specific requirements that differ from standard postal format.

Apartment numbers on checks, contracts, and official documents

On checks and legal documents, use the same format as your mailing address. Write your apartment number after the street address, on the same line or on the line below. This ensures that any mail sent to that address — including bank statements, legal notices, or lease renewals — reaches the right unit.

When you sign a lease or rental agreement, the address section should already have your apartment number filled in. Verify that it matches exactly what is on your mailbox and what you have given to your landlord. If there is a discrepancy, ask the landlord to correct it before you sign. A wrong address on a lease can cause problems if you ever need to enforce your rights as a tenant or if the landlord needs to serve you with a notice.

Frequently Asked Questions

Should I write "Apartment" or "Apt" on official documents?

Both are correct. "Apt" is shorter and more common on forms and envelopes. "Apartment" is fine on contracts and formal documents. The postal service and online systems accept both. Use whichever your landlord or the form asks for, or stick with "Apt" if you have a choice.

What if my apartment has both a number and a letter, like 4B?

Write it exactly as it appears on your lease and mailbox: "Apt 4B" or "Unit 4B". Do not separate the number and letter. The postal service and address systems treat "4B" as a single unit identifier.

Can I use a pound sign (#) instead of "Apt"?

Yes. "#4B" is accepted by the postal service and most online forms. It is shorter and works well on envelopes and forms with limited space. Use it consistently if you choose it.

What happens if I forget to include my apartment number?

Mail may be delivered to the building's main office, held at the post office, or delivered to the wrong unit. If you have already given an address without the apartment number to a bank, employer, or government agency, update it as soon as possible. Contact them directly and provide the correct address with the apartment number included.

Does the apartment number go before or after the city and state?

The apartment number always comes after the street address but before the city and state. The correct order is: street address, apartment number, city, state, zip code. Never put the apartment number after the zip code or before the street address.