Suppose that on the first floor of a building, there are three separate apartments numbered 1, 2 and 3 respectively. How can I refer to one of them when writing a postal address? I am wondering if there is any need to mention words like "apartment" or "unit" before the apartment number. Which one is more appropriate to use?

"Apartment 2, first floor"
"Unit 2, first floor"
"2, first floor"
"2 first floor"
"2 1st floor"

I also found this entry on Wikipedia which suggests that the words "lot" and "unit" can be used before the apartment number in Malaysia. (My question is more about American English though):

Salutation, Name of recipient
Name of Position & Department (if applicable)
Company name
Unit/Lot number, Building name/Commercial area
Lot number (for building), Street name
Postcode Post office/Mail centre
State (optional)


Lot 323, 1st Floor, Bintang Commercial Centre

Any advice would be appreciated.

  • 1
    The correct address format is usually defined by the national postal service and it would be appropriate to use that form regardless of the language being used. Examples: addressdoctor.com/en/countries-data/address-formats.html Commented Feb 8, 2013 at 15:27
  • It would be quite unusual to require the floor number as well as apartment number. Usually the appartments in the building will all have unique numbers. So it could be the first floor has apartments 1,2,3 and the second floor has apartments 4,5,6. Or, more common nowadays, the first floor would have 11,12,13 and the second floor would have 21,22,23. Or 2A, 2B, 2C.
    – GEdgar
    Commented Sep 25, 2016 at 12:49
  • In the US, postal regulations pretty much require that a given apartment/office within a multiple-tenant building be expressed with a single designator. This designator could be a simple string of numbers or letters, numbers/letters connected with a dash, etc. Often the floor number is encoded in the designator, but one need not know that to send a letter. Of course, other countries will have different rules, and I seriously doubt that there's a single protocol that will cover all nations. (For a more specific answer you need to first identify the destination country.)
    – Hot Licks
    Commented Sep 25, 2016 at 14:19

4 Answers 4


If you haven't received an address, then any of those should be understood, not seem rude, and get the message to its intended recipient, which is after all the entire point of the exercise.

If you've got an address from someone, then use the form they gave no matter how far from the formats you give seems; it might relate to some preference within the building or of the addressee. Just as with a name, you should use what the recipient prefers, even if it seems strange or silly to you.

(Your fourth does have the minor disadvantage of lacking a comma to help mentally space the number from the floor).

  • 1
    Thank you. Please tell me which one is more common to use where you live.
    – B Faley
    Commented Feb 8, 2013 at 11:44
  • 2
    I've seen all of those, also "Apt" as an abbreviation, and "Flat". I use Irish English though, rather than American, though the only strong difference I'm aware of is that they tend not to use "flat" as a word for a one-floor apartment.
    – Jon Hanna
    Commented Feb 8, 2013 at 11:47
  • 3
    AmE doesn't use flat for apartment at all unless we're trying to sound posh (i.e., British). "Apt" is commonly used as an address abbreviation in the US.
    – Kit Z. Fox
    Commented Feb 8, 2013 at 11:56
  • @Kit, ironically some in the UK and Ireland favour apartment over flat, to sound, if not quite posh, then at least more affluent. Probably influenced by the apartments of relatively wealthy characters on US television shows or favouring the French appartement over the Old English flet. These differences point to what I said about favouring what the addressee uses if you know it.
    – Jon Hanna
    Commented Feb 8, 2013 at 12:02
  • 1
    I'd strongly recommend putting in a word like "Apartment", "Unit", "Suite", or so on. This definitely makes it clearer what you mean. (So either of your first or second addresses.) Which one of these is correct depends on what the actual building management calls them, but they should all be understood. In the U.S., "Apartment" would be used mainly in residential buildings, and "Suite" in office buildings. "Unit" is much less common, but could be used for either. Don't use "Lot"; it won't be understood. Commented Feb 8, 2013 at 12:34

If you're looking for the official answer, the USPS lays out standards for addressing unit numbers.

123 Main St Apt 2

City ST 12345

If you're not exactly sure, you can use this tool to enter as much information as you have, and it will convert it to the correct format. (Example)


In American English, for simply a residential apartment, you'd likely use a number sign, like this:

My Friend Flicka
#3, First Floor
87654 First Avenue
City, ST Zip+4

Often though, the apartment follows the street address, like this:

My Friend Flicka
87654 First Avenue #3
City, ST Zip+4

My Friend Flicka
87654 First Avenue Apt. 3
City, ST Zip+4

And occasionally but infrequently immediately follows the street address, but this seems to usually be when the apartment is a letter:

My Friend Flicka
87654-B First Avenue
City, ST Zip+4

"Lot" is generally not used except for trailer park or industrial/business park addresses. "Unit" is used and is recognizable, in particular for business addresses and apartment complexes with multiple buildings.

"Suite" is also sometimes used, but generally for business addresses.

  • 2
    The 87654-B convention is often used if a house (for example) is letting some rooms as an apartment. For example, I live at 16473, and the in-law apartment over the garage, which I let, has the address 16473-A. Commented Feb 8, 2013 at 13:33

There is no standard as to how to label separate dwelling or commercial units within a building, whether it consists of a single or multiple floors. If you own the building (or control it), you get to name it.

Several schemes are common in the US.

Commercial buildings

Single floor The most common approach is to label units with Arabic numerals or capital letters. These are usually preceded by the terms Unit, Suite, No. or the symbol # (the last two being more common when only numerals are used).

Multifloor A very common approach is to label units with the floor number followed by a unit number or letter, with or without a hyphen. In the US, the ground floor is generally referred to as 1. The same preceding labels are used as in single floor buildings. For example, a unit on the second floor might be called

  • Unit 2B
  • Unit 22
  • Unit 2-2
  • Suite 2B
  • No. 22
  • No. 2-B
  • #2-2
  • #2-B

Less common is Floor 2, Unit B or its variations listed above.

In smaller multifloor buildings, the same labeling system may be used as in single storey buildings, without giving specific reference to floors, especially when there are fewer than 10 units.

Residential Buildings The same schemes are used as in commercial buildings, but the term Apt (for Apartment) is more commonly used than Unit or Suite. One or more of the highest floors may be referred to as Penthouse or PH with or without a numeral or capital letter.

A period may or may not be used in the abbreviations listed above.

In each of these, when listing an address, the street address is listed first and the unit identifier is list next, on the same line, separated by a comma, as in

John Doe
123 Commerce St., Apt. 3-G
New York, NY 10025

  • 1
    Actually, there's 200 pages worth of standards about how you write postal addresses.
    – josh3736
    Commented Feb 8, 2013 at 15:51
  • @josh3736 which contemplates most of the above variations, adds Room and Ste (for Suite, not to be confused with female French Saints) and shows preferrences for no period, block capitals and avoiding #. But the vast majority of addresses written do not strictly hew to the USPS guidances.
    – bib
    Commented Feb 8, 2013 at 16:37

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