Two buyers comparing projects on the same arterial road in north Bengaluru in early 2026 noticed something odd. One tower rose slim and tall with generous gardens around it, while another packed far more flats onto a similar sized plot with barely a strip of open ground. Neither was breaking a rule; they were simply built to different densities, and the number that governs that difference is one most buyers never ask about. It is called the floor space index, and understanding it explains why two plots of similar size can carry very different buildings.

The short answer. Floor space index, also called floor area ratio, is the ratio of the total built up floor area allowed on a plot to the size of the plot itself, and it is fixed by the local planning authority. In Bengaluru that is broadly the city corporation within its limits and the development authority for its layouts, and the permitted figure depends on factors such as road width and zone. The trade-off to accept: a higher density can mean more homes and sometimes a lower price per unit, but it can also mean less open space and more pressure on shared amenities, so density is a quality of life question, not just a number.

What is FSI or FAR?

Floor space index, or FSI, is the ratio between the total built up floor area of a building and the area of the plot it stands on. In India the terms floor space index and floor area ratio, or FAR, mean the same thing, so you can treat them as interchangeable. The index is a planning tool that controls how much can be built on a given piece of land, which in turn shapes the height, the density and the feel of a development.

For a buyer, the value of understanding FSI is that it explains the character of a project before you even step inside. A low index tends to go with more open ground and lower density, while a high index allows more floor area and often taller, denser buildings. Neither is good or bad in the abstract; what matters is that you understand which one you are buying into and whether it suits how you want to live. Families wanting greenery and quiet may lean one way, while those prioritising a central location at a keener price may accept more density in return.

How is FSI calculated?

FSI is worked out by dividing the total built up floor area of a building by the area of its plot. If a plot measures a thousand square metres and the permitted index is one and a half, then the maximum built up floor area allowed is one thousand five hundred square metres, because a thousand multiplied by one and a half gives that figure. A higher index allows more floor area on the same land.

The permitted index itself is not a single fixed number across a city. It is set by the planning rules and can depend on factors such as the width of the abutting road, the size and shape of the plot and the zone it sits in, so two nearby plots can carry different permitted figures. Because of this variation, the number that applies to a specific project comes from its approved plan and the applicable local regulations, not from a general rule of thumb.

Who sets FSI in Bengaluru?

In Bengaluru the permitted index is governed by the local planning bodies, broadly the city corporation and the development authority. Areas within the corporation limits are regulated by the Bruhat Bengaluru Mahanagara Palike, while outlying areas and planned layouts fall under the Bengaluru Development Authority. The applicable index for a given site flows from these bodies and the planning regulations that apply to that location.

For a buyer, the practical takeaway is that the permitted index is a matter of official record for the specific plot, not something to be taken from a brochure. What a developer is allowed to build is set by the sanctioned plan and the regulations behind it, so the reliable source is the approval, cross checked against the project registration, rather than a marketing claim about density or height.

Why does FSI matter to a flat buyer?

FSI matters because it shapes both the living environment and the legality of what is built. The index controls how many homes and how much floor area a project can offer on its land, which affects open space, light, and the load on shared amenities and local infrastructure. A denser scheme can be perfectly legal and still feel more crowded, so knowing the density you are buying into helps you judge whether it fits your life.

How does FSI connect to unauthorised construction?

The link is direct: floors built beyond the permitted index can be treated as unauthorised. If a developer constructs more floor area than the sanctioned plan and the applicable index allow, that excess can be considered a deviation, with the same risks that attach to unauthorised construction generally, from stop work concerns to problems with loans and title. This is why the index is not just a planning abstraction but a practical safeguard for a buyer.

Because of this, comparing the building on site against its sanctioned plan matters as much for FSI as it does for the number of floors. If a project appears to pack in far more than its approvals should allow, that is a question to raise, not a feature to admire. The safe habit is to rely on the approved plan and the project registration rather than assuming that whatever has been built must have been permitted. What stands on site is not proof of what was sanctioned, and only the approval and the record can settle that question for you.

What should a buyer check about FSI?

Focus on the approved plan and the project record rather than trying to compute the index yourself. Ask the builder for the sanctioned plan and confirm the built up area and floors align with what was approved, and cross check the project against its RERA registration. If a scheme is notably dense, look into the road width and surroundings, since these can affect both the permitted index and the everyday experience of living there.

You do not need to become a planning expert to use FSI wisely. The core discipline is simple: treat the permitted density as something recorded in the approvals, judge whether the density suits you, and be cautious where a building appears to exceed what its plan allows. Where anything looks out of step, a property lawyer or a qualified professional can read the approvals against the regulations for you.

How does FSI fit with the rest of due diligence?

FSI is the density lens of due diligence, and it works best beside the area, approval and registration checks. Knowing the permitted density tells you about the character and legality of the built form, but not the usable area of your own flat or the cleanliness of the title, so it belongs alongside those rather than in place of them. A rounded view for a Bengaluru buyer reads the density, the usable area and the approvals together.

Pair this with our guide on RERA carpet area versus super built up area, and our explainer on the difference between an occupancy and a completion certificate. If you are weighing a specific project, you can also review a listing such as this Bengaluru project. Together, density, usable area and approvals give you a fuller sense of what you are buying.

Your seven step FSI checklist

1. Ask the builder for the sanctioned plan and the permitted floor area for the project.
2. Confirm the built up area and number of floors match what the plan approves.
3. Cross check the project details against its RERA registration.
4. Note whether the scheme is low or high density and whether that suits you.
5. Look into the road width and surroundings for a notably dense project.
6. Treat floors that appear to exceed the approvals as a question, not a feature.
7. Where anything looks out of step, have a professional read the approvals.

Frequently asked questions

What is FSI or FAR in simple terms?

Floor space index, or FSI, is the ratio of the total built up floor area allowed on a plot to the area of the plot itself. Floor area ratio, or FAR, means the same thing in India. It is a planning tool that controls how much can be built on land, which shapes height, density and open space.

How is FSI calculated?

FSI is the total built up floor area of a building divided by the area of its plot. For example, a plot of one thousand square metres with a permitted index of one and a half allows a maximum built up area of one thousand five hundred square metres. A higher index allows more floor area on the same land.

Who decides the permitted FSI in Bengaluru?

The local planning bodies do. Areas within the corporation limits are regulated by the Bruhat Bengaluru Mahanagara Palike, while outlying areas and layouts fall under the Bengaluru Development Authority. The permitted index for a specific site comes from these bodies and the planning regulations, and it can depend on factors such as road width, plot size and zone.

Why should a buyer care about FSI?

Because it shapes both the living environment and the legality of the building. A higher index means more homes and often less open space, while a lower one usually means more breathing room. Floors built beyond the permitted index can be treated as unauthorised, so density affects both quality of life and safety.

Last updated 2026-07-16. PropNewz Team.