Suite/Unit Number
A secondary address element that identifies a specific unit within a multi-tenant building, such as an apartment, suite, floor, or room.
Secondary address designators are essential for accurate delivery in multi-unit buildings. The USPS recognizes a set of standard abbreviations: APT (apartment), STE (suite), UNIT, FL (floor), RM (room), DEPT (department), and others. In a properly formatted address, the secondary designator appears on the same line as the street address (preferred) or on a separate line immediately above it.
Including the correct secondary designator is critical for delivery point validation. Without it, mail may be returned as undeliverable or left in a building's common area. Automated sorting equipment uses the secondary address to generate a delivery point barcode that identifies the exact recipient within a building.
The pound sign (#) is sometimes used as a generic secondary designator, but the USPS discourages its use because it can cause processing errors in OCR systems.