Correctly Addressed

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How to address an envelope to an apartment

Put the apartment number at the end of the street line, not on a line of its own. Write it as 1420 N BROADWAY APT 4B. Use APT, not Apartment and not the pound sign. The Postal Service reads the line just above the city line as the delivery line, so anything sitting on its own line above the street can be treated as extra information and skipped.

Checked July 30, 2026/7 min read

Claire Post

Written by Claire PostReviewed against USPS Publication 28

What is on this page7 sections
  1. 01Step by step
  2. 02Real examples
  3. 03Quick reference
  4. 04Special cases
  5. 05Key terms
  6. 06Check before you mail
  7. 07Questions people ask

An apartment address has one extra piece of information in it, and where you put that piece decides whether the letter arrives.

The Postal Service reads an envelope from the bottom up. The last line is the city, state and ZIP. The line directly above it is treated as the delivery line, and that is the line the carrier works from. Anything above that is treated as extra.

So an apartment number sitting alone on its own line, above the street, is in the wrong place. The machine reads the street as the delivery line and the unit becomes a note.

Step by step

  1. Start with the name on the mailbox

    Use the name the building has on file. A nickname the carrier does not know can be enough to send a letter back in a building with a lot of turnover.

  2. Put the unit at the end of the street line

    Street number, direction, street name, then the unit. All on one line, no comma.

    JORDAN REYES1420 N BROADWAY APT 4BDENVER CO 80202
    CorrectThe format the scanner is built to read.

  3. Use the short form of the word

    APT for apartment, STE for suite, UNIT for unit, RM for room, FL for floor, PH for penthouse, BSMT for basement. Spelling it out is not wrong, but the short form is what the address file holds.

  4. Only use a second line if the street line runs out of room

    If the whole thing will not fit, the unit goes on the line above the street, never below it. The line right above the city is always read as the delivery line.

    JORDAN REYESAPT 4B1420 N BROADWAY EXTENSIONDENVER CO 80202
    CorrectThe fallback, for long street names only.

A few real examples

The steps above cover the rule. These show it applied to a spread of real situations, so you can match yours to the closest one.

JORDAN REYES1420 N BROADWAY APT 4BDENVER CO 80202
CorrectStandard apartment, unit as a number.
JORDAN REYES1420 N BROADWAY PHDENVER CO 80202
CorrectA penthouse unit. PH goes exactly where APT would.
JORDAN REYES1420 N BROADWAY BSMTDENVER CO 80202
CorrectA basement unit in a converted building.
JORDAN REYES1420 N BROADWAY BLDG 3 APT 12DENVER CO 80202
CorrectA complex with numbered buildings, each holding numbered units.

Quick reference

Pin this next to your printer
You wantWriteDo not write
ApartmentAPT 4BApartment 4B, #4B
SuiteSTE 300Suite 300, Ste. 300
UnitUNIT 12Unit #12
FloorFL 33rd Floor
RoomRM 210Room 210
PenthousePHPenthouse, PH#
Basement unitBSMTBasement, Bsmt.
Building and unitBLDG 3 APT 12Building 3, Apt 12 (on its own line)

Special cases

The rule above covers most people. Here is what changes for the rest.

What if the complex has numbered buildings and each building has numbered units?

Put both on the street line, building first: 1420 N BROADWAY BLDG 3 APT 12. This is the one case where two unit designators appear back to back, and it is correct as long as both stay on the street line, in that order, with no line break between them.

What about a floor-only address, with no separate unit number?

FL and the number, same placement as any other designator: 1420 N BROADWAY FL 3. This is common in small walk-up buildings where each floor is its own unit rather than being subdivided into lettered apartments.

Does a basement apartment need anything special?

No special handling beyond using BSMT in place of APT. If the basement unit also has its own number, write it as BSMT 1 the same way you would write APT 1.

Key terms on this page

Secondary address
The part of an address that narrows a street address down to one unit inside a larger building, such as an apartment, suite, or floor number.
Unit designator
The short code identifying what kind of secondary address it is: APT, STE, UNIT, RM, FL, PH, or BSMT.
Delivery line
The line directly above the city, state and ZIP line. This is the line a carrier actually reads to sort and deliver mail, which is why a unit sitting on a separate line above it can get treated as extra information.
Address file
The USPS database of every known deliverable address, including the standard abbreviations it expects for each secondary address type.

Check the address before you mail

Questions people ask

Is the pound sign really a problem?
It is allowed, but APT is cleaner. The pound sign is one of the characters scanners misread most often, and it tells the machine nothing about what kind of unit it is.
What if the building uses letters instead of numbers?
Write it exactly as the building does. APT B and APT 4B are both fine. Do not add a number the building does not use.
Does this apply to a suite in an office building?
Yes. A suite follows the same rule as an apartment. STE goes at the end of the street line.
Is PH the correct abbreviation for a penthouse, or should I just write Penthouse?
PH is the standard short form and the one the address file recognizes. Writing out Penthouse in full is not wrong, but it adds characters the scanner has to process for no benefit, the same tradeoff as writing Apartment instead of APT.

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