What does gross area mean?

Gross area is the total floor area of a building measured to the outside face of its exterior walls. It includes the walls themselves and every space inside them, finished or not, on every floor.

The word gross works the way it does with income: it is the whole amount before anything is taken out. Net area is what remains after deductions, usually the space inside the walls that people can actually use.

For houses, the more useful number is gross living area. It is still measured from the outside of the walls, but ANSI Z765 limits it to finished living space above ground. A house with a big garage and a basement can have a gross area far larger than its gross living area, and the appraisal reports that extra space on separate lines.