A measure of area in the Imperial System, the acre is composed of 43,560 square feet. The area itself need not be square and can take any shape. It is is commonly used to describe land parcels in the real estate market. Larger parcels of land may also be described in terms of square miles. It takes 640 acres to make one square mile.

The historical origins of the acre may have roots in early agriculture. It is thought an acre was the amount of land that could be tilled by a man and an ox in one day.