The square footage for which rent can be charged. It may be calculated in several ways, including:

• BOMA (International Association of Building Owners and Managers)- From the inside of the outside wall (or in new buildings, from the glass line), to the outside of the inside wall (or hall-walls) and center to center on the division walls. Columns are to be included.
• GSA (General Services Administration)- Same as BOMA, except all columns, division walls, services closets, and other service areas are included. Net usable space only. This method is typically used when leasing to the federal government.
• New York Method- Space is measured right across the floor from the glass line, subtracting only the elevator shafts and stairwells. Where there are multiple occupancies on a single floor, the common space in its entirety (including both usable and non-usable) is apportioned among the tenants according to the size of their respective areas.