Usable vs. Rentable Square Feet

Understanding the space you occupy—and the space you pay for.

When comparing commercial spaces, you may see square footage described as gross, usable, or rentable. These measurements serve different purposes, and understanding the distinction helps you compare properties and calculate occupancy costs.

We will frequently reference BOMA—the Building Owners and Managers Association International. BOMA publishes widely used measurement standards for commercial real estate. Different standards apply to different property types, so office, industrial, and retail space may be measured differently. The explanation below focuses primarily on multi-tenant office buildings.

Gross Area: The Overall Building

Gross area generally describes the overall building area measured to the outside face of its exterior walls. It includes wall thickness and areas beyond the individual tenant suites.

BOMA distinguishes between different area measurements, including Exterior Gross Area and Construction Gross Area. A gross-area measurement is sometimes used as the leasing basis for a building occupied entirely by one tenant.

Tenant Tip: Square footage alone does not tell you whether a space will work. Review the floor plan and consider circulation, columns, room sizes, and how efficiently your team can use the layout

Usable Area: Your Exclusive Space

For everyday leasing discussions, usable square feet (USF) describes the space reserved for your exclusive use—the offices, reception area, conference rooms, storage, and other areas within your suite.

Think of it as the space where your business operates.However, usable area is a measured area, not simply the open floor space available for furniture. Wall boundaries and other measurement rules depend on the applicable standard and edition.

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Rentable Area: Your Space Plus an Allocation of Shared Areas

Rentable square feet (RSF) generally includes your exclusive space PLUS an allocated share of qualifying common and service areas.

These may include shared lobbies, corridors, restrooms, elevators and building amenities. The applicable measurement standard determines which areas are included and how they are allocated.

These shared spaces support your use of the building—even though they are outside your suite.

Tenant Tip: Ask for both the usable and rentable square footage, along with the load factor. Two suites advertised as 1,150 rentable square feet may provide different amounts of exclusive space.

Load Factor: Connecting Usable and Rentable Area

The load factor expresses the relationship between usable and rentable area. It may be stated as a multiplier, such as 1.15, or as an additional percentage, such as 15%.

Here is a simple example:

Measurement	Square Feet
Usable space	1,000
Shared-area allocation: 15% of usable space	150
Rentable space	1,150

1,000 USF × 1.15 = 1,150 RSF

In this example, your business occupies 1,000 usable square feet, while rent is calculated on 1,150 rentable square feet.

What Does This Mean for Your Rent?

Commercial office rent is commonly quoted per rentable square foot. If the example above rents for $30 per RSF annually, the annual base rent would be:

1,150 RSF × $30 = $34,500 per year, or $2,875 per month.

Under a NNN lease, operating-expense charges may also be quoted per rentable square foot. However, the lease determines the calculation, the tenant’s proportionate share, and which expenses are recoverable.

The shared-area allocation recognizes that tenants benefit from more than their individual suites. The landlord also provides and maintains the spaces that allow the building to function.

Understanding usable and rentable square footage helps you look beyond the advertised size and rate. For tenants, it supports better space and budget decisions. For landlords, clear measurements and consistent explanations create transparency from the first tour through lease signing.

As always, not all landlord’s or leases are the same so be sure to ask questions!