FSI or floor space index is the upper limit to the built space you may construct on a given plot. It is the ratio of allowed built-up area to the plot area. For example, on a 10,000 ft2 plot which has an FSI of 2, you may construct a maximum of 20,000 ft2 of area, and no more. FSI can also be called FAR or floor area ratio. Certain types of spaces, such as basements, parking areas, and utility rooms, are exempt from FSI, which means that they do not need to be counted in the FSI calculations.