What is Floor Space Index, Formula & Why is it Important?
The floor space index plays a key role in maintaining population density in urban areas and city planning. Floor space index is expressed in the form of a ratio between floor area and plot area. This is also known as Floor Area Ratio in some locations.
What Is a Floor Space Index?
Floor space index is a value derived from a comparison done between a building's total floor area and plot area. This helps engineers to calculate the maximum number of floors that can be built on that piece of land. The area taken up by floors is also known as the built-up area.
Going forward in this blog, you will also know the key deciding factors and importance of floor space index. You will also be given the formula and illustration on the same for better understanding.
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What Is the Floor Space Index Formula?
Following given is the formula for computation of floor space index:
Floor space index (FSI) or floor area ratio (FAR) = total built-up area / total area of the plot
Total built-up area= total area of plot X FSI allotted
For a clearer understanding, an illustration of FSI calculation is given below:
Suppose there is a plot of an area of 10,000 square metres. FSI of 1.5 is permitted. Then, the construction of a total of 15000 square metres will be allowed on that piece of land. This is also applicable to commercial buildings.
| Plot of the area | 10,000 square metres |
|---|---|
| FSI permitted | 1.5 |
| Permitted construction area | 15,000 square metres (10,000*1.5) |
What Is a Premium Floor Space Index?
Premium floor space index is applicable to those plots which have an adjacent main road. Here, the width of the road is also considered while calculating floor space index of that plot. However, there are some conditions regarding premium floor space index, which are mandatorily followed by the constructors. They are as follows:
- The minimum width of the road must be of 30 feet.
- If width of the road is anywhere between 30 ft. and 40 ft., then constructors can avail of 20% more FSI.
- When the width of the road is around 40 to 60 ft., constructors can have 30% more floor space index.
- If the width of the adjacent road exceeds 60 ft., a builder can have 40% more FSI.
| Minimum road width | 30 feet |
|---|---|
| FSI of roads 30-40 feet wide | 20% more |
| FSI of roads 40-60 feet wide | 30% more |
| FSI of roads wider than 60 feet | 40% more |
What Is the Importance of Floor Space Index?
Floor space index is a piece of knowledge, which is equally important for buyers and real estate developers. The value of FSI is calculated and determined by the local municipalities for a plot of land. Usually, the larger the plot, the higher the building construction. So, there is a chance that you will have a higher number of neighbours who will share the same amenities as you, such as parks, jogging area, gaming centre, sports club, gym, and elevators living in a project with high FSI.
FSI differs from one city to another, but it will not exceed the maximum limit of 2.5. FSI is determined keeping in mind the population density of that area, open spaces, environmental effect on the surroundings and occurrence frequency of natural disasters.
What Are the Factors That Decide the Floor Space Index?
Given factors affect the floor area ratio of a particular plot of land.
- Area of the plot
- Population density of that area
- Accessibility to water, electricity, and sewage
- Type of building, residential or commercial
- Availability of open space
- Environmental impact of the real-estate
- Eventuality and readiness in time of natural disaster
What Are the Components of Floor Space Index (FSI)?
While determining the floor space index of construction, there are two major components. They are basic and fungible floor space indexes. Accumulation of these two decides the maximum legitimate FSI for a particular plot.
Basic FSI: This variation comes free of cost
Fungible FSI: This has to be bought from the local municipal authority. This is decided depending on the Ready Reckoner Rate or Circle Rate of that area as determined by the local authority. This is what makes the difference between the FSIs of different cities.
Floor Space Index for Top Cities in India
In the following table, you will get to know about the minimum and maximum floor space index for some of the important cities in India as determined by their respective local authorities:
| Local Authority | Residential FSI | Commercial FSI |
| Kolkata Municipal Corporation | 1.25-3 | 2-3 |
| Municipal Corporation of Greater Mumbai | 1-4 | 1-5 |
| Bruhat Bengaluru Mahanagar Palike | 1.75-3.25 | 1.5-3.25 |
| Noida Authority | 2.75-3 | 1-4 |
| Chennai Metropolitan Development Authority | 2-4.87 | 0.75-1.5 |
Frequently Asked Questions
Which spaces are not included in the calculation of total floor area?
Balconies, parking lots, garages, covered walkways and driveways, patios, outdoor spaces, attics, and outdoor sports courts are not included in the calculation of total floor area.
What is considered to be a good floor area ratio?
The higher the floor area ratio, the more space available for construction. Hence, most developers prefer high FAR. But this entirely depends on the city and the condition of the locality within that city.