Floor Area Ratio Calculator

Floor area ratio is the total gross floor area of a building divided by the area of the lot it stands on, a dimensionless number that measures bulk without dictating form. A FAR of 1.0 on a 10,000 square foot parcel permits 10,000 square feet of floor area, which could be one story covering the entire lot, two stories covering half of it, or a ten story tower on a tenth of it. That neutrality is the whole point: FAR caps development intensity while leaving massing to setback, height, and coverage rules that operate alongside it. Lot coverage is the separate measure of ground-floor footprint as a share of the parcel, and a project generally has to satisfy both limits. Typical ranges in United States zoning run about 0.3 to 0.5 in single-family districts, 0.75 to 2.0 in multifamily, 1.0 to 2.5 in neighborhood commercial, and 5.0 to 15.0 or higher in central business districts. The same concept is called plot ratio in the United Kingdom and Australia and floor space index in India. The principal caveat is definitional rather than mathematical: what counts as floor area varies by jurisdiction. Most codes measure to the exterior face of walls and exclude below-grade cellars, unenclosed balconies, rooftop mechanical space, and frequently structured parking, and many offer density bonuses of 10 to 25 percent for affordable units, public plazas, or proximity to transit. Two physically identical buildings can therefore post different FAR figures under different ordinances.

Zoning in the United States began with height and setback controls rather than with ratios. New York City adopted the first comprehensive ordinance in 1916, after the bulk of the Equitable Building cast a shadow across lower Manhattan, using a setback envelope that produced the familiar wedding-cake skyscraper profile. The Supreme Court upheld municipal zoning generally in Village of Euclid v. Ambler Realty Company in 1926, and the Standard State Zoning Enabling Act circulated by the US Department of Commerce during the 1920s let states delegate the power broadly to local governments. Floor area ratio displaced the envelope approach when New York City overhauled its code in the 1961 Zoning Resolution, a rewrite shaped by modernist tower-in-a-plaza thinking. Rather than sculpting a building from the outside, the 1961 code assigned each district a permitted FAR and offered bonus floor area in exchange for providing a public plaza at ground level. Other American cities adopted the metric quickly, and it spread internationally under local names, including floor space index in Indian development control rules and plot ratio in British and Commonwealth practice. Later planning scholarship, particularly criticism of the plaza bonus and the barren spaces it produced, has focused on how crudely a single ratio captures the urban design outcomes cities actually care about, which is why FAR is almost never used alone.