FSI / FAR (Floor Space Index)

Floor Space Index (FSI) — called Floor Area Ratio (FAR) in many states — is the ratio of the total built-up floor area of all floors of a building to the area of the plot on which it stands. An FSI of 2.0 on a 500 m² plot permits 1,000 m² of total floor area. It is the single most important development-control parameter, set by each city's Development Control Regulations / building bye-laws and varying with road width, land use, and zone.

Many states offer 'premium FSI' (purchasable), 'TDR' (transferable development rights) and incentive FSI for affordable housing, redevelopment or green buildings. Certain areas — staircases, lift wells, services, basement parking, refuge floors — are typically exempt from FSI. The NBC 2016 Part 2 provides the administrative framework while the binding numeric limits come from the local authority's DCR.