Floor Area Ratio Calculator

Floor Area Ratio (FAR), often used interchangeably with Floor Space Index (FSI), is calculated by dividing the total built-up area of all floors by the total land area of the plot. The fundamental equation is expressed as FSI = TotalBuiltUpArea / TotalLandArea. To arrive at the total built-up area, the tool sums the built-up footprints across all units, factoring in individual unit footprints, internal partition walls, and designated common structural zones. Additional foundational equations include CarpetArea = IndoorArea - WallsArea, BuiltupArea = CarpetArea + WallsArea, and SuperBuiltupArea = BuiltupArea + (CommonArea / Units), ensuring every tier of architectural measurement is accurately accounted for.

Consider a multi-family residential development built on a total land area of 5,000 square meters. The project consists of 10 identical units. For a single unit, the indoor area measures 90 square meters, and the interior walls take up 10 square meters. First, we calculate the carpet area: CarpetArea = 90 - 10 = 80 square meters. Next, we determine the built-up area by adding the walls back: BuiltupArea = 80 + 10 = 90 square meters. Multiplying this by the total number of units gives the total built-up area: TotalBuiltUpArea = 90 * 10 = 900 square meters. Finally, to find the Floor Area Ratio, we divide the total built-up area by the total land area: FSI = 900 / 5,000 = 0.18, or an 18% floor area ratio.

Always verify local municipal guidelines, as different cities classify open balconies, stilt parking, and basements differently when calculating final FAR. Ensure that all area inputs use consistent units—mixing square feet and square meters will skew your calculations immediately. When planning developments, leave a comfortable buffer below the maximum allowable FAR limit to account for minor architectural adjustments during the permitting phase.