Historically, the amount of land a yoke of oxen could plow in one day;today,a quantity of land containing 43,560 square feet.An acre can be any shape.Especially in the case of commercial properties,land values are usually expressed in terms of price per square foot rather then price per acre.
Example: If you know that a 16-acre parcel recently sold for $10,000,000, you calculate the price per foot as follows:
16 acres 43,560 square feet per acre 696,960 square feet
$10,000,000 696,960 feet $14.35 per square foot