A buyer in Bengaluru liked a compact apartment block on a narrow road, where the builder had squeezed in a couple of extra floors and priced the flats keenly. Everything looked complete and lived in. What the buyer did not check was how much floor area the plot was actually allowed to carry, and whether the building stayed within it. The extra floors that made the project affordable were also the ones that pushed it past what the plan permitted, which turned a bargain into a flat in a partly unauthorised building. The number that would have told him this was not on the brochure. It was a ratio, set by the rules for that plot, that quietly decides how much a building may lawfully be.

The short answer. FSI, the Floor Space Index, and FAR, the Floor Area Ratio, are two names for the same thing, the ratio of a building's total built up area to the area of its plot, and it decides how much can lawfully be built. In Bengaluru the base figure runs roughly from 1.25 to 3.25 depending on the zone, the plot size and the width of the road, with extra floor area available on some plots through premium FAR. For a buyer the check is simple to state, that the building's built area stays within the FSI sanctioned on its approved plan, because anything beyond that is unauthorised construction and carries regularisation, khata and loan risks. The trade off is that the projects which stretch the FSI hardest are often the cheapest, for exactly that reason.

What is FSI or FAR?

FSI and FAR are the same planning measure, and both express how much building a plot is allowed to carry. The Floor Space Index, also called the Floor Area Ratio, is the ratio of the total built up floor area of a building, added up across all its floors, to the area of the plot it stands on. So an FSI of 2.0 on a plot of 500 square metres allows a total built up area of 1,000 square metres, whether that is spread over two large floors or four smaller ones. It is, in effect, the budget of floor area a plot is given, and a building has to fit within it. This is why FSI is the number that ultimately limits how tall or how dense a project can be on a given piece of land, more so than the height alone. For a buyer, understanding FSI is understanding the ceiling on what could lawfully be built where your flat is, which is the reference point against which the actual building should be measured.

How is FSI decided in Bengaluru?

In Bengaluru the FSI for a plot is set by the building rules, and it varies with the zone, the plot size and the width of the road the plot faces. The city's building bye laws, administered by the municipal corporation, fix a base FSI that for residential plots runs roughly from 1.25 to 3.25, with the exact figure depending on those factors. The width of the abutting road matters in particular, because a wider road generally allows a higher FSI, on the logic that it can support a denser building. On top of the base figure, some plots can access additional floor area through premium FAR, extra entitlement that can be availed on certain plots, notably along metro and transit corridors, taking the permissible floor area higher still. The practical point for a buyer is that the FSI available to a plot is not a single citywide number but one specific to that plot's zone and road, and it is set by the rules rather than chosen by the builder. What the builder can lawfully construct is bounded by that figure, as reflected in the sanctioned plan.

What does FSI look like at a glance?

The table below sets out the key facts about FSI as they bear on a buyer.

Reading the table, the first rows explain what FSI is and how it is set, and the last is the one that protects a buyer, that the building as constructed should sit within the FSI its plan was sanctioned for. The base range and the premium entitlement matter because they tell you what was possible on the plot, but the decisive question is whether the actual building stayed inside what was approved. A project can have a perfectly ordinary FSI on paper and still be built beyond it, which is the situation a buyer needs to catch.

Why does FSI matter to a buyer?

FSI matters to a buyer for two reasons, one about the feel of the project and one about its legality. On the first, a higher FSI allows a denser building, more flats on the same land, which shapes the number of neighbours, the pressure on lifts and parking, and the general feel of the development, so it is part of understanding what living there will be like. On the second, and more importantly, the sanctioned FSI is the line between authorised and unauthorised construction. A building that stays within the floor area its plan was approved for is lawful on that count, while one that exceeds it has built more than the plan allowed, which is a deviation. This is where FSI stops being an abstraction and becomes a risk, because unauthorised floor area is not a cosmetic issue. It can affect the building's approvals, its occupancy certificate, the khata for the flats and a bank's willingness to lend. For a buyer, then, FSI is both a lifestyle input and, more seriously, a legality check.

What happens if a building exceeds its sanctioned FSI?

A building that exceeds its sanctioned FSI has unauthorised construction, and that carries consequences that fall on the flats within it. Construction beyond the approved floor area is a deviation from the sanctioned plan, and depending on its extent it may not be regularisable, which leaves the excess exposed to action by the authority. The knock on effects are what reach a buyer. Excess unauthorised area can stand in the way of a clean occupancy certificate, complicate the khata for the flats, and make a bank reluctant to lend against a unit in the building. In the more serious cases the unauthorised portion faces a demolition risk, and even where it does not, the cloud over the building depresses resale value because the next buyer runs the same check. None of this is visible by looking at the flat, which is precisely why it is missed. The way to catch it is to compare the building as built against the floor area its plan was sanctioned for, rather than to assume that a finished, occupied building must therefore be a compliant one.

How do I check FSI on a project?

Work through these steps when weighing a project or a flat.

1. Ask for the sanctioned plan and the floor area it approves for the building.
2. Note the plot area and work out the FSI the sanction corresponds to.
3. Check that figure against the base FSI expected for the zone and road width.
4. Confirm any additional floor area was availed as premium FAR, not simply built.
5. Compare the building as constructed against the sanctioned floor area for excess.
6. Treat unauthorised floor area as a risk to the occupancy certificate, khata and loan.
7. Raise any excess with the builder and verify it before you commit to the flat.

How does this fit plan deviation and area checks?

FSI is the measure that a deviation is judged against, so it sits at the centre of the same enquiry. A building that exceeds its sanctioned FSI is precisely the deviation we cover in our guide to checking a building plan deviation before buying, and the floor area concepts connect to the difference between what you pay for and what you can use, which we set out in our explainer on carpet area, super built up area and the loading factor. For a flat in a project such as Aparna Wonderwoods at Mallasandra, the sanctioned FSI is what bounds how much the building could lawfully be. FSI, plan deviation and the area you actually get are three views of the same building, and reading the FSI is how you check that the building the brochure sells is the one the plan allowed.

Frequently asked questions

What is FSI or FAR? They are two names for the same planning measure, the ratio of a building's total built up floor area, added across all floors, to the area of the plot. An FSI of 2.0 on a 500 square metre plot allows 1,000 square metres of built up area. It is the budget of floor area a plot is allowed.

What is the FSI in Bengaluru? For residential plots the base FSI runs roughly from 1.25 to 3.25, set by the building bye laws and varying with the zone, the plot size and the width of the abutting road, with a wider road generally allowing more. Some plots can access additional floor area through premium FAR, notably along transit corridors.

Why does FSI matter when buying a flat? Because the sanctioned FSI is the line between authorised and unauthorised construction. A building within its approved floor area is lawful, while one that exceeds it has built more than the plan allowed, a deviation that can affect the occupancy certificate, the khata and a bank's willingness to lend. A higher FSI also means a denser building.

What if a building has exceeded its sanctioned FSI? The excess is unauthorised construction, a deviation that may not be regularisable and can face action by the authority. For a buyer it can complicate the occupancy certificate, the khata and the home loan, depress resale value, and in serious cases carry a demolition risk. Compare the building against its sanctioned floor area.

Last updated 2026-08-31. PropNewz Team.