An acre-foot is a unit of volume commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, and river flows. Definition It is defined by the volume of one acre of surface area to a depth of one foot. Since the area of one acre is defined as 66 by 660 feet (a chain by a furlong) then the volume of an acre-foot is exactly 43560 cubic feet. Alternatively, this is approximately or 1,233.5 kL (or m³). Discussion As… (More on Acre-foot)