The number of units refers to the quantity of separately sold or separately let spaces within a structure. It normally applies to multi-tenant residential buildings, hotels, hospitals, and retail centers.

A multi-room suite (e.g. in a hotel or hospital) is considered a single unit unless it consists of adjacent rooms which are normally rented singly.

The normal sale or letting arrangement determines the unit boundary. Several rooms supplied together as one suite contribute one unit, while rooms normally let separately can contribute several.