Floor area, also known as floor space, is the area taken up by a building or part of it, measured as square feet or square meters. The definition of floor area depends on what factors of the building should or should not be included, such as external walls, internal walls, corridors, lift shafts, stairs, etc. . There are generally three major differences in measuring floor area:

• Gross floor area (GFA): The total floor area contained within the building measured to the external face of the external walls.
• Gross internal area (GIA): The floor area contained within the building measured to the internal face of the external walls.
• Net internal area (NIA): The usable area within a building measured to the internal face of the external walls, excluding areas such as corridors, stairwells, and toilets.

Floor area ratio (FAR) is another term related to floor area, which is the relationship between the total amount of usable floor area that a building has and the total area of the lot on which the building stands. FAR is expressed as a decimal number and accounts for the entire floor area of a building, not simply the buildings footprint. Excluded from the square footage calculation are unoccupied areas such as basements, parking garages, stairs, and elevator shafts. The floor area ratio is a key determining factor for development in any country, and a higher ratio usually indicates a dense or highly urbanized area.