# Floor space index

Floor space index (FSI)is also called the Floor area ratio.

It is the ratio of the total floor area of buildings on a certain plot to the size of the total area on that location. In a formula we can put it as:

Floor area ratio/floor space index= total area covered on all floors of a building/area of the plot.

In simpler words we can say that a floor space index of 2.0 would imply that the total floor area of a building is two times the gross area of the plot.

## Floor space index used in zoning

The floor space index is used in zoning to define a limit of the total construction that can be done on a plot. Let’s take an example to further explain this. If the zoning permitting authority permits 0.1 floor space index, then in such a case, the total area of all floors can only be limited to one-tenth of the total area of the plot.

Now herein an architect can either plan for a single storey building utilising the entire allowable area in one floor or a multi storey building that rises higher above the surface of the plot. By combining both horizontal and vertical limits in a single figure more flexibility is allowed in the building design while getting a harder limit on at least one measure of overall size. One advantage here to fix this parameter is that the floor area correlates well with other parameters such as the total parking for commercial use or the total number of units for residential use or total load on municipal services. The amount of these things remains constant irrespective of how that area is divided horizontally or vertically. This is the reason why the authorities find it necessary to include limitations on height too when using floor space index.