Understanding the formula for calculating house construction costs and the Floor Space Index (FSI) is crucial for effective project planning. Construction cost is typically estimated by multiplying the total built-up area by the cost per square foot. FSI, also known as Floor Area Ratio (FAR), is calculated by dividing the total built-up area by the plot area. For instance, if a plot spans 1,000 square meters with an FSI of 2, the permissible built-up area would be 2,000 square meters.