An acre-inch of water is a unit of measurement used to describe the volume of water needed to cover an acre of land to a depth of one inch. This unit is commonly used in the field of irrigation and water management to determine the amount of water needed to adequately hydrate crops and plants.
One acre-inch of water is equivalent to 27,154 gallons of water, or about 3.3 acre-feet. This may seem like a large amount of water, but it is actually a small fraction of the water that is needed to irrigate a typical acre of land. For example, a single acre of corn can require up to 25 acre-inches of water per year, while an acre of alfalfa can require as much as 40 acre-inches.