The ratio of a building's total gross floor area to the size of the land area of the lot. Jurisdictions often use FAR in zoning codes to:

For example, if a zoning ordinance allows construction on a property with a maximum FAR of 0.20, then the total area of all floors in all of the buildings constructed on the property cannot exceed two-tenths of the total area of the property itself.

In some jurisdictions, if a building is underbuilt, so that the building's total floor area is less than the maximum FAR allowed, a property owner may transfer the property's excess FAR to another property owner with no available FAR. The purchaser of the excess FAR can then use the additional FAR to increase the size of the building situated on its land.