Most appraisers use a simple technique to determine gross living area (GLA). They measure the exterior of the home. If the exterior measures 30 feet by 40 feet and is one story, the home contains 1200 square feet. This includes all closets, hallways, stairwells, and even wall space since its starting from the exterior. The appraiser will also take into consideration other finished spaces not included in the square footage but usually at a lower price per square foot than the main house.