What is FSI in Real Estate and How to Calculate it?

FSI stands for “floor space index”. It is also called “floor area ratio” (FAR) in real estate. It is the ratio between the area of the covered floor (the built-up area) and the overall area of the plot upon which the building or the construction stands.

FSI is important when you’re talking about real estate. If you’re confused what it is and how it must be taken into consideration when buying a home or a real estate property, we are going to demystify it in this write-up. You will learn what it means and how it is calculated.

Although FSI and FAR mean the same thing, FSI is calculated in percentage and FAR in decimals.

FSI for the same measurement of a building may differ from city to city, and sometimes even from one locality to another. Sometimes it can vary within the same location, based on the number of floors a building has. It is regulated depending on the type of building, the number and quality of amenities your residential complex has, and the city zone.

How do you calculate it?

It is calculated by dividing the total floor area of all the floors of the building by the total plot area, multiplied by 100.

Here is an example:

Suppose a building is constructed over an 800 square feet plot.

Being a multi-storeyed building, it has different floors and if you add all the areas of all the flaws, it comes up to be 1600 square feet.

FSI = 1600 (total area of all the floors) / 800 (area of the plot) X 100

= 200%

Why is this important?

It tells you how much floor area you can have in a locality or a zone. Once you have a plot to construct a building on, it doesn’t mean you can just randomly build floors upon floors. There may be a limit to how many floors you can build on a specific plot.

Depending on your Floor Space Index you need to decide

• How many floors there can be in a building.
• What the size of the floors can be.
• How many apartments can be built on each floor.

As a buyer, this can have an impact on how big a flat you can own in a locality, and based on the amenities available, what price you’re going to pay.

You can find the zone FSI on your state government’s official website.

Using the inverse FSI calculation illustrated above you can calculate how much covered area can be built.

Suppose the FSI is 1.5 in your chosen zone.

The plot area is 4000 square feet.

The covered area that can be built is 4000 x 1.5 = 6000 square feet.

Depending on how many floors are permissible, a building can have three floors of 2000 square feet each or two floors of 3000 square feet each, or another variation within the confines of the FSI.

What is premium FSI?

Premium FSI is applicable if a real estate property is by the side of a road. You can pay a premium to the government and get extra floor space area. How much premium FSI can be obtained depends on the width of the road. Below given calculation is applicable:

• 30-50 feet width road: 20% extra than the allowable FSI.
• 40-60 feet width road: 30% extra than the allowable FSI.
• More than 60 feet width road: 40% extra than the allowable FSI.

Here is an example:

The allowable FSI is 1.5.

The plot is 3000 square feet.

The road width is 48 feet.

Allowable built area is 3000 x 1.5 = 4500 square feet.

Since the width of the adjacent road is 48 feet, 30% extra built area is allowed to be constructed.

4500 x 30/100 = 1350 square feet.

Total built area: 4500 + 1350 = 5850 square feet.

Should you know the FSI before buying an apartment?

Definitely, you should know the FSI of the flat. FSI violation usually comes to light when a completion certificate is issued by the development authority. Therefore, when buying a property make sure that you ask for a completion certificate because it contains all the details about the allowable FSI. In case there have been some violations, and you end up buying the property despite those violations, you may need to bear the repercussions. You may even be stuck with the property and will not be able to sell it. In case you have some issues with the property, the resolution will be difficult because it will be a disputed property.

Therefore, it is important to know the allowable FSI in your zone/locality, and also whether the property you are investing in abides by the bylaws or not.