To understand how to calculate carpet area, measure the internal length and width of each usable room and multiply them. Then, add the area of all bedrooms, living rooms, kitchens and bathrooms. Carpet Area = Length × Width of Each Usable Space For example, a 12 ft × 10 ft room has a carpet area of 120 sq. ft. Repeat the same process for every room to get the total measurement. When checking what is RERA carpet area, remember that it includes internal partition walls but excludes external walls, balconies, terraces, service shafts and common spaces. The difference between RERA carpet and actual carpet may occur because actual usable floor space can be slightly lower. Buyers should also understand what is built up area, what is super built up area and the basic built up area calculation before comparing properties.