Square footage is measured from outside wall to outside wall. If you measured from insidewall to inside wall your results will be smaller. For example, let's say that a house is 40 feet by 50 feet and has a wall thickness of six inches. Outside wall to outside wall is 40' times 50',or 2,000 square feet. Inside wall to inside wall would be 39.5' times 49.5', or 1,955 square feet.
Square footage is only a method of comparing one property with another.
Other features arealso used. In commercial appraisal,properties are compared by such things as number of rooms, number of apartment units and evencubic feet. Nevertheless, it is true that inresidential real estate square footage is the most common measurement of comparison. I know that the appraiser looks at similar properties to compare to the one being appraised,but I understand there are other measurementsthat are used. The first is the one where similar properties are compared.