In the second calculator, assuming that your entry values were in feet, the number of surface acres is returned, along with the number of acre-feet and acre-inches of water volume, based on the entered depth. Both are units used to measure volumes of water, typically for use in irrigation. One acre-foot is the volume of water sufficient to cover an acre of land to a depth of 1 foot, is equal to 43,560 cubic feet, approximately 325,851 U.S. gallons (approximately 1233.48 cubic meters). At year 2000 considering American rates of consumption, on average 1 acre-foot of water is enough to meet the industrial and municipal demands of 4 people for a year. An acre-inch, the volume of water needed to cover an acre to a depth of 1 inch, 1/12th of an acre-foot, is approximately 27,154.25 gallons or approximately 102.79 cubic meters.