Different organizations use the term “square feet” to mean different things. At NIH, square feet are measured in three ways, depending on the use to which the measurements are put. The diagrams and definitions below clarify the terms used by NIH.

On this page:
Net Assignable Square Feet
Rentable Square Feet
Gross Square Feet
Square Foot Rule of Thumb

These diagrams illustrate the components of rentable and gross square feet in the building. At top right is a floor plan of a typical floor in a representative building. Below it is a cross-section of the building showing mechanical rooms.

Net Assignable Square Feet (nasf):
The area of a floor or office suite that is suitable for occupancy including secondary corridors found within locked tenant areas. It excludes shared space such as main egress corridors, hazardous waste marshaling areas on the loading dock, and other non-programmable space. In calculating nasf no deduction is made for columns and projections that are necessary to the building.

In contrast, Architects/Engineers often use the term Net Square Feet (nsf) to mean anything they must design. This area often includes the non-programmable space listed above.

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Rentable Square Feet (rsf):
Rentable Square Feet are the sum of Net Assignable Square Feet and the square feet of common areas on the floor (floor common) or in the building (building common). These areas typically include restrooms, break rooms, public corridors, lobbies, closets (LAN, telephone, housekeeping), mechanical/electrical rooms, and loading docks. Rentable square feet are calculated for a given IC by adding the IC’s Net Assignable Square Feet and a percentage of the common areas based on the nasf the IC occupies in the building. This definition is used in charging rent.

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Gross Square Feet (gsf):
The total area in a building for all floors to the outer surface of exterior walls. Gross square feet includes all research and administrative space, retail space, and other areas such as vending machine space and storage. Gross Square Feet also includes Major Vertical Penetration areas greater than two square feet, such as shafts, elevators, stairs, or atrium space. This figure is used in defining construction costs for facilities.

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Square Foot Rule of Thumb:
In research space, Net Assignable Square Feet equal about 50% of Rentable Square Feet.
In administrative space, Net Assignable Square Feet equal about 85% of Rentable Square Feet.