What is floor space index (FSI)?
Floor space index (FSI), or floor area ratio (FAR), is the total floor area a plot may be built to, divided by the plot’s area. An FSI of 2 on a 1,000 sq m plot allows 2,000 sq m.
Also called FSI, floor area ratio, FAR.
FSI caps how much can be built on a plot. It is set by the development control regulations of the state or planning authority, so the numbers differ from city to city, and often by road width and zone within a city. More FSI means more floor area on the same land.
Example: Maharashtra (UDCPR 2020). The Unified Development Control and Promotion Regulations apply to every planning authority in the state except Greater Mumbai, MIDC, NAINA and a few other areas. They define FSI as the area covered by the “P line” on all floors (Regulation 6.6) divided by the net plot area. Basic FSI is what a plot gets without paying a premium or loading TDR. On top of it, a builder may buy premium FSI and load TDR, up to a cap that rises with the width of the road the plot faces.
For residential and mixed-use buildings in the non-congested areas of municipal corporations, Table 6-G sets:
| Road width | Basic | Premium | TDR | Maximum |
|---|---|---|---|---|
| Below 9 m | 1.10 | – | – | 1.10 |
| 9 m to below 12 m | 1.10 | 0.50 | 0.40 | 2.00 |
| 15 m to below 24 m | 1.10 | 0.50 | 0.90 | 2.50 |
| 30 m and above | 1.10 | 0.50 | 1.40 | 3.00 |
The premium for premium FSI is 35% of the land rate in the annual statement of rates. Ancillary area FSI of up to 60% of the proposed FSI (80% for non-residential use) can be added on payment of a further premium.
Worked example (sample figures). A 2,000 sq m net plot on an 18 m road in a municipal corporation, in a non-congested area:
| Component | FSI | Built-up area |
|---|---|---|
| Basic | 1.10 | 2,200 sq m |
| Premium FSI (bought) | 0.50 | 1,000 sq m |
| TDR (bought) | 0.90 | 1,800 sq m |
| Maximum on the plot | 2.50 | 5,000 sq m |
That is before ancillary area FSI and any extra FSI under special schemes in Chapter 7. Where part of the plot is handed over for a development plan road, reservation or amenity space, basic FSI is worked out on the land the owner keeps, while premium FSI and TDR may use the whole plot.
How it differs from carpet area. FSI is a limit for the whole plot. The carpet area is the net usable floor area of one flat under the RERA Act.
Sources, read on 9 Nov 2026: UDCPR 2020, updated to 30 Jan 2025 (Directorate of Town Planning, Maharashtra) and the RERA Act (Gazette copy hosted by MahaRERA).