Real estate appraisal

A real estate appraisal is an appraiser's opinion of what a property is worth, usually its market value. Most home appraisals are ordered by a lender before it approves a mortgage.

Size is one of the main facts an appraisal rests on. The appraiser compares the home with recent sales of similar homes nearby, and gross living area is the figure used to line those sales up. Differences in size then turn into adjustments to the comparable sales.

That is why measuring rules matter. If one house is measured with its basement and another without, the comparison breaks. ANSI Z765 exists so that appraisers measure every house the same way.

Further reading: Real estate appraisal on Wikipedia.