Floor Area
Floor area is the amount of horizontal surface inside a building, usually given in square feet or square meters. It can describe one room, one storey or the whole building, and it is one of the most common figures used to describe the size of a home.
There is no single floor area. Gross floor area is measured to the outside faces of the exterior walls and includes the space the walls occupy. Net or usable floor area is measured inside the walls. Other versions leave out stairwells, shafts or unfinished space depending on the purpose.
Building codes, zoning rules, leases and property records each pick the version that suits them, which is why two documents can list different areas for the same building.
Before comparing two figures, check which floor area each one uses. A residential appraisal in the US reports gross living area, which is measured from the exterior and counts only finished, above-grade space.
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