The acre-foot is a non-SI unit of volume equal to about 1,233 m3 commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, irrigation water,[1] and river flows.

As the name suggests, an acre-foot is defined as the volume of one acre of surface area to a depth of one foot.

On December 31, 2022, the National Institute of Standards and Technology, the National Geodetic Survey, and the United States Department of Commerce deprecated use of the US survey foot and recommended conversion to either the meter or the international foot.

Water reservoir capacities in the US are commonly given in thousands of acre-feet, abbreviated TAF or KAF.

Large bodies of water may be measured in cubic kilometers (1,000,000,000 m3, or 1000 gigaliter), with 1 million acre-feet approximately equalling 1.233 km3.