FSI = Total built-up floor area of all floors / Plot area
Measure the total floor area covered by all constructed floors
Measure the total area of the plot or land
Divide the total built-up floor area by the plot area
Use the formula: FSI = Total Built-up Area ÷ Plot Area
Example: if built-up area = 2,000 sq ft and plot area = 1,000 sq ft, then FSI = 2.0