The standard apartment abbreviation is Apt., capitalized and ending in a dot, as in "Apt. 3C." On envelopes and packages, the Postal Service prefers the same letters in all capitals without a period, APT. The plural is Apts., which you will see in rental listings and building directories.
Apt. tells a mail carrier, a delivery driver or a landlord exactly which unit inside a building you mean. Leave it off and a package can end up in the lobby, or back with the sender.
Quick facts
Standard form
Apt.On mail
APT, all capitals, no periodPlural
Apts.Symbol option
# before the unit number, as in # 3CUsed in
Addresses, leases, rental listings, formsAvoid
Appt., which means appointment
Every common apartment abbreviation compared
| Form | Where it fits | Notes |
|---|---|---|
| Apt. | Letters, forms, leases, signs | The everyday choice in American writing |
| APT | Envelopes and shipping labels | Postal style uses capitals with no punctuation |
| Apts. | Listings and building names | "Willow Creek Apts." or "two apts. available" |
| # | Address lines | Stands in for Apt. when no other unit word is used |
| apt | Texts and notes | Casual, no capital or period |
All of these point to the same idea. For anything formal or official, use Apt. or APT and add the unit number right after it.
Where Apt. goes in an address
Postal style puts the unit at the tail end of the street line, right after the street name. If that line is too long, it can go on the line just above.
A properly written envelope:
JORDAN LEE
1450 RIVER RD APT 12B
SPRINGFIELD IL 62704
Here APT 12B tells the carrier which mailbox in the building gets the letter.
Online forms often give you a separate box labeled "Address line 2" or "Apt, suite, unit." Type the unit there, for example "Apt 12B." Do not use both Apt. and # together, as in "Apt. #12B"; one or the other is enough, and the unit word is clearer when you know it.
What does apt stand for?
On an address, apt stands for apartment. A few other meanings exist, and context makes them easy to separate:
- Apt as a word: in ordinary English, apt is an adjective meaning suitable or likely, as in "an apt description" or "apt to rain." It is not an abbreviation there.
- APT in computer security: advanced persistent threat, a long running, well funded hacking campaign.
- Apt. in a listing: always apartment, often next to bedroom counts such as "2 BR apt."
Apt. vs appt. and other unit words
The biggest mix up is with appt., which shortens appointment. One p means apartment; two p's mean appointment. Our page on the appointment abbreviation covers that one in detail.
Apartments are not the only units with short forms. The Postal Service lists several unit words, each with its own code:
| Word | Mail form | Typical building |
|---|---|---|
| Suite | STE | Offices, medical buildings |
| Unit | UNIT | Condos, townhomes, storage |
| Building | BLDG | Large complexes with several buildings |
| Floor | FL | Office towers |
| Room | RM | Dorms, hotels, schools |
See the suite abbreviation and the building abbreviation pages for more.
Periods, capitals and plural forms
- Period: add one in regular writing, Apt., because letters were cut from the end. Skip it on postal labels.
- Capital: capitalize it before a number ("Apt. 7") and in a building name ("Maple Grove Apts."). In a sentence such as "she rents an apt. downtown," lowercase is fine, though spelling out apartment reads better.
- Plural: Apts., with the s before the period.
- Spoken aloud: people read Apt. 4 as "apartment four," never as the word apt.
Sentences that use the abbreviation
- "Deliver to 22 Pine St., Apt. 5, after 6 in the evening."
- "Pine View Apts. has two units open next month."
- "Apt. or suite number (optional)" on a checkout page.
- "Leave the key with the manager in Apt. 1A."
- "Sunny 1 BR apt. near the bus line, pets allowed."
Need the short form of another address or paperwork word? Try the common abbreviations section.
Questions people ask
Should I write Apt or # in my address?
Either works, but use only one. Apt. is clearer because it names the type of unit, while # simply says a unit number follows.
What is the abbreviation for apartment?
The abbreviation for apartment is Apt. On mail and shipping labels, the Postal Service style is APT in capitals with no period.
What is the plural of Apt.?
The plural is Apts. You will see it most often in apartment complex names and in rental ads listing more than one unit.
Is apt short for appointment?
No. Apt. means apartment. Appointment is shortened to appt., with two p's, so keep them separate to avoid confusion.
Where do I put the apartment number on an envelope?
Put it at the end of the street line, as in 1450 River Rd Apt 12B. If it will not fit, write it on the line directly above the street address.