How To Write An Apartment Address So Mail Arrives and Landlords Find You

The standard format for an apartment address

An apartment address follows this order: your name, street number and name, apartment number, city, state, and ZIP code. Each line goes on its own. The apartment number comes after the street address on the same line, or on the line below — both are correct. The U.S. Postal Service (USPS) prefers the apartment number on the same line as the street, separated by a space or comma.

Here is what it looks like:

Sarah Martinez 1247 Oak Street, Apt 3B Denver, CO 80202

Or, written the other way:

Sarah Martinez 1247 Oak Street Apt 3B Denver, CO 80202

Both formats work. The key is that the apartment number appears somewhere on the address so mail carriers and delivery services know which unit to enter. Without it, mail may go to the building's main office or get returned.

Key Takeaways

Write your apartment number after the street address on the same line, or on the line directly below it — USPS accepts both formats.
Use "Apt" or "#" before the number; do not use "Apartment" spelled out, as it takes up space and is unnecessary.
The city, state, and ZIP code always come last, on their own line.
If your building uses unit numbers instead of apartment numbers, write it the same way — the format works for any unit designation.

Where the apartment number goes

The apartment number is part of the street address line, not a separate address. Write it when ready after the street name and number. You can use "Apt," "Apartment," "#," or "Unit" — USPS recognizes all of them. The shortest versions ("Apt" and "#") are preferred because they save space on envelopes and forms.

Do not put the apartment number on the same line as the city and state. That line is reserved for the city, state, and ZIP code only. If you run out of space on a form and have to choose between leaving out the apartment number or leaving out the ZIP code, leave out the apartment number — the ZIP code is what the postal system uses to sort mail first. But whenever possible, include both.

Abbreviations and formatting

Use these abbreviations for apartment designations:

Apt — the most common abbreviation for apartment
# — a single symbol that means "number" or "unit"
Unit — spelled out, used in some buildings instead of "apartment"
Ste — abbreviation for "suite," used in office buildings or commercial addresses

Do not spell out "Apartment" in full on mailing addresses. It wastes space and is not necessary. On official documents like a lease or rental agreement, you may see it spelled out, but for addresses on envelopes, packages, and forms, use the short version.

Capitalize the first letter of the abbreviation. Write "Apt 3B," not "apt 3B." The apartment number itself can be letters, numbers, or both — "Apt 5," "Apt 3B," "Apt 201" are all correct.

What to do if your building does not have apartment numbers

Some older buildings or small complexes use only street addresses without unit numbers. If your building has no apartment number, use the street address alone. However, tell your landlord and the post office that your building lacks unit numbers. The post office may assign one for mail delivery purposes, or they may note your building in their system so carriers know to deliver to a specific entrance or mailbox.

If you are receiving mail at a building with no apartment number and it keeps going to the wrong unit, contact your local post office branch directly. Bring your lease or a piece of mail addressed to you. The carrier can note your specific location — for example, "rear unit" or "upstairs" — in their delivery notes so future mail reaches you.

Apartment addresses on forms and online

Online forms and rental applications often have separate fields for "Street Address" and "Apartment/Unit Number." When you see these fields, put the street number and name in the first field, and the apartment number in the second field. Do not repeat the street address in the apartment field.

If a form has only one address field and no separate apartment field, write the full address on one line: "1247 Oak Street, Apt 3B." If the form asks for a mailing address and a separate physical address, use the same format for both unless your mailbox is in a different location than your unit — for example, if your mailbox is in the building lobby but you live on the third floor.

Common mistakes to avoid

Do not put the apartment number in parentheses, like "1247 Oak Street (Apt 3B)." The postal service reads parentheses as secondary information and may not process the apartment number correctly. Write it with a comma or space instead: "1247 Oak Street, Apt 3B" or "1247 Oak Street Apt 3B."

Do not write the apartment number before the street address. "Apt 3B 1247 Oak Street" is incorrect and will confuse mail carriers. The street address always comes first.

Do not use special characters or punctuation in the apartment number itself unless your lease shows them that way. If your unit is "3-B," write it as "3-B," not "3B." Match what appears on your lease and mailbox.

Frequently Asked Questions

What if I do not know my apartment number?

Check your lease, your mailbox, or the outside of your door — the number should appear in at least one of these places. If you cannot find it, ask your landlord or building manager. They can tell you the official unit number used for mail and official documents.

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

Yes. The pound sign (#) is a standard abbreviation for "number" or "unit" and USPS accepts it. Write it as "#3B" or "# 3B." Both work. Choose whichever fits your space or preference.

Does the apartment number go before or after the city?

The apartment number goes with the street address, before the city. The format is: street address and apartment number on one or two lines, then city, state, and ZIP code on the final line. The city and state always come last.

What if my building uses letters instead of numbers for units?

Write it the same way. "Apt A," "Apt B," or "Unit 201C" all follow the same format. The postal service does not care whether your unit is a number, letter, or combination — as long as it appears in the address, mail carriers can find you.

Should I include the apartment number on a package label?

Yes, always include it. Delivery services like UPS, FedEx, and Amazon use the apartment number to route packages to the correct unit. Without it, packages may be left at the building entrance or returned to the sender.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.