The building area is 80 square meters. How much is the practical area?

The building area is 80 square meters. How much is the practical area?

Generally speaking, there are three kinds of housing area indicators: building area, built-in area and practical area. Built in area: the horizontal projection area of the space used by the built-in housing. Built in area: equal to the built-in area + built-in wall area + built-in balcony area. Built in area: built-in area + shared area