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, and river flows.

Definition

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It is defined by the volume of water necessary to cover one acre of surface area to a depth of one foot. It is equal to exactly 43,560 cubic feet, or nearly 325,851 U.S. gallons, or approximately 1233.48 cubic meters.

Discussion

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As a rule of thumb in U.S. water management, one acre foot is taken to be roughly the amount of water used annually by a family of four (844.8 liters of water, per person, per day). The acre foot (or more specifically the time rate unit of acre foot per year) has been used historically in the U.S. in many water-management agreements, for example the Colorado River Compact, which divides 15 million acre feet per year (586 m³/s) among seven western U.S. states.

Customary units in the United States

acre-foot | エーカー・フィート