Why is the square footage on my appraisal different from the listing?

Usually because the two numbers measure different things. The appraiser measures gross living area under ANSI Z765, which leaves out basements, garages, and unfinished space. A listing often uses a number from tax records, the builder, or the seller that may include them.

The most common gaps are a finished basement counted in the listing, a garage picked up from the assessor's building area, and a finished room reached only through the garage or by a ladder. Each one is real space, but none of them is gross living area.

Smaller differences come from how the house was measured. An appraiser measures to the outside of the exterior walls and rounds only at the end, so two careful measurements usually land within 1 to 2 percent of each other. A gap of 10 percent or more almost always means someone counted a space differently.