$/ac·ft

per acre-foot

Cost per volumeexact by definition

Cost per acre-foot, the volume covering one acre to a depth of one foot, exactly 1233.48183754752 cubic metres or about 325851 US gallons. It is the unit of water rights, allocations and wholesale water pricing across the western United States, and the conversion is exact since both the acre and the foot are exactly defined.

1 $/ac·ft 0.00081071319 $/m³
Where the unit came from

An acre-foot is roughly what a suburban household uses in a year, which is why allocations and reservoir volumes are quoted in it: the number is directly readable as a number of households served.