Floor area ratio

Floor area ratio, or FAR, is a building's total floor area divided by the area of the lot it sits on. A 2,000 square foot house on a 10,000 square foot lot has a floor area ratio of 0.2.

Local rules often use FAR to cap how much building can go on a lot. The floor area in that math follows the local rule's own definition, which may count garages, basements, or other space that gross living area leaves out.

So FAR and gross living area are different numbers for different jobs. FAR is about how much building a lot can hold. Gross living area, measured under ANSI Z765, is about how much finished living space a house has, and it is the figure an appraiser uses to compare homes.

Further reading: Floor area ratio on Wikipedia.