In a nutshell, usable square footage is the actual space you occupy from wall to wall. Usable square footage does not include common areas of a building such as lobbies, restrooms, stairwells, storage rooms, and shared hallways. For tenants leasing an entire floor or several floors, the usable square footage would include the hallways and restrooms exclusively serving their floor(s).
Rentable Square Feet
Rentable square footage is your usable square footage PLUS a portion of the building’s shared space. As mentioned above, shared space can be anything that is outside of your occupied space and is of benefit to you (lobbies, restrooms, hallways, etc). As a tenant in a commercial space, you pay for a portion of the shared space and thus your monthly rent is always calculated on RSF.
The increase in the the rentable square footage above your usable square footage is referred to variously as the “load factor,” “common area factor,” or “add-on factor.” This is generally in the 10-15% range and can be higher in some buildings. When evaluating commercial real estate space options, you’ll want to be aware of this factor so you know exactly what you’re getting and what you’re paying for.
How to Calculate Load Factor
Calculating the load factor is pretty straightforward. First, find out how much total floor area a building has. Then, subtract the shared square footage to determine the usable square footage. The owner or owner’s agent should be able to give you these numbers. Then divide the total floor space by the USF to get the load factor.
Example: A 100,000 square foot building has 15,000 square feet of shared space. The usable square footage is 85,000 square feet. The load factor would be 1.176 (100,000 / 85,000). That would also be the same as saying the building has a load factor of 17.6%.