The area of an acre is 43,560 square feet. If an acre is shaped in a perfect square, each side is about 209 feet long. The perimeter equals the sum of the lengths of each side, or approximately 836 linear feet. If the acre's perimeter is circular, the number of linear feet equals the circumference of the plot, or 740 feet. Acres with irregular sides have perimeters of different lengths based on their particular shape.