FSI Calculator — Floor Space Index (FAR)

FSI (Floor Space Index), also called FAR (Floor Area Ratio), is the total built-up area you may build divided by the plot area. Enter your plot and the FSI your authority permits and the tool returns the maximum built-up area, the footprint per floor and how many floors fit — or switch modes to find the FSI of a design you already have. Permissible FSI is set locally, so you enter your own value; the ranges and rules below tell you what to expect and what to confirm.

What FSI (FAR) actually is

FSI is a single ratio that caps how much floor you can build on a plot:

FSI = Total built-up area of all floors ÷ Plot area

On a 1,200 sq ft plot with a permitted FSI of 1.5, you may build 1,800 sq ft of total built-up area — across as many floors as the height rules and ground coverage allow. FSI says nothing about how many floors; it caps the total floor area. Two floors of 900 sq ft or three of 600 sq ft both use an FSI of 1.5 on that plot. For the meaning and history of the term, see what is Floor Space Index.

How to calculate FSI — worked example

Take a 1,200 sq ft plot with a sanctioned FSI of 1.5 and 50% ground coverage:

• Maximum built-up area = 1,200 × 1.5 = 1,800 sq ft
• Footprint per floor = 1,200 × 50% = 600 sq ft
• Floors that fit = 1,800 ÷ 600 = 3 floors (a ground + 2, i.e. G+2)

So the plot supports a G+2 house of 600 sq ft per floor, 1,800 sq ft in all. Push the coverage down to 40% (480 sq ft footprint) and the same 1,800 sq ft would need close to four floors instead — FSI fixes the total, coverage and height decide how it stacks.

Typical FSI by plot and road — confirm locally

FSI is not a national number. It is set by each city's development control regulations and shifts with plot size, the width of the abutting road, the zone, and any premium FSI or TDR loaded on top. The ranges below are indicative only — always read the sanctioned figure from your local authority or architect before designing.

Because the spread is real, the calculator never assumes a limit for you — you type the value your authority sanctions and it does the arithmetic.

Ground coverage and setbacks

Ground coverage is the share of the plot the building footprint may occupy after leaving the required setbacks (the open margins on each side). A plot with 50% coverage keeps half its area open. FSI and coverage work together: coverage limits the footprint, FSI limits the total floors, and the height regulation limits how tall you go. A plot can hit its coverage limit and still have FSI left, which is what pushes a house upward. The open area you leave also drives light, ventilation and parking, so it is regulated separately from FSI.

Premium FSI, fungible FSI and TDR

Many cities let you build beyond the base FSI by paying for it or buying development rights:

• Premium FSI — extra FSI bought from the authority against a fee, usually tied to road width.
• Fungible / compensatory FSI — additional area (often ~35% in some cities) that can be added, typically on payment, to enclose balconies, flower beds and voids.
• TDR (Transfer of Development Rights) — FSI generated elsewhere (e.g. where land was surrendered for a road) and loaded onto your plot within limits.

These stack on the base FSI up to a ceiling. The calculator handles any of them — just enter the total permissible FSI after premiums.

FSI vs carpet, built-up and super built-up area

FSI is computed on built-up area, not carpet area. Built-up is the covered area including walls; carpet is the usable floor inside; super built-up adds a share of common areas. Getting these confused is the most common FSI mistake — see carpet area vs built-up area for the exact difference. Once you know your permissible built-up area, price the actual construction on the home construction cost calculator and check room dimensions against standard room sizes.

Frequently asked questions

What is the full form of FSI? FSI stands for Floor Space Index. It is the ratio of a building's total built-up area to the plot area, and is the same thing as FAR (Floor Area Ratio).

How do I calculate FSI? Divide the total built-up area of all floors by the plot area. For example, 1,800 sq ft of built-up area on a 1,200 sq ft plot gives an FSI of 1.5. To find the maximum area you may build, multiply the plot area by the permissible FSI instead.

Is FSI the same as FAR? Yes. FSI (Floor Space Index) and FAR (Floor Area Ratio) are two names for the same ratio of built-up area to plot area. Indian regulations use both terms interchangeably.

What is a good FSI for a residential plot? There is no single good value — it is whatever your local authority permits. Base residential FSI in India commonly falls between 1.0 and 2.0, rising to 3.0 or more with premium FSI and TDR in dense zones. Always confirm the sanctioned figure for your specific plot.

Does FSI decide the number of floors? No. FSI caps the total built-up area, not the floor count. How many floors you build depends on the ground coverage and the height regulation. A lower ground coverage spreads the same FSI over more floors; a higher coverage over fewer.

Is balcony area counted in FSI? It depends on the city. Many authorities exclude a portion of balconies, voids and service areas from FSI, or allow them under fungible/compensatory FSI on payment. Check your local development control rules for exactly what is counted.