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. It is defined by the volume of one acre of surface area to a depth of one foot. Since the acre is defined as a chain by a furlong ($66 ft \times 660 ft$) the acre-foot is exactly $43,560 cubic feet$. For irrigation water, the volume of $1 ft \times 1 \; ac = 43,560 \; ft^{3} (1,233.482 \; m^{3}, 325,851 \; US gal)$.
Acre Foot