How to Format Apartment, Suite and Unit Numbers

Address basics  |  April 7, 2026  |  2 min read

Missing or misplaced unit numbers are one of the most common reasons packages are delayed at large buildings. The fix is simple once you know where the secondary information belongs.

Put the unit at the end of the street line

The preferred format places the unit designator and number after the street: 850 PINE ST APT 12. This keeps everything the carrier needs on one line.

If the line is too long

When a label or form limits line length, move the unit to its own line directly above the street line:

• APT 12
• 850 PINE ST

Do not place it below the street line, because sorting machines expect the city, state and ZIP after the delivery line.

Use the right designator

• APT for apartments
• STE for suites in office buildings
• UNIT for condominiums and storage units
• FL for floors, as in FL 3
• RM for rooms, as in RM 204

If you are unsure, the pound sign with a space works: 850 PINE ST # 12.

Letters and fractions

Units can include letters, such as APT 4B, and some addresses have fractional house numbers like 12 1/2 ELM ST. Your form should accept both, so test with them.

Designing the form field

Most checkout forms use an "Address line 2" field for units. Label it clearly, keep it optional and store it separately from the street line so you can format it either way when printing labels. Our generator adds a random unit to about one in five addresses so you can see both cases.