A half acre equals to 21,780 square feet. About 43,560 square feet make one acre. To convert acres into square feet, the number of acres is multiplied by the conversion factor. In this case, 0.5 acres is multiplied by 43,560 square feet.
An acre is a unit of area primarily used in the imperial and U.S. customary measurement systems. It is equal to 4,047 square meters, 4,840 square yards, 0.405 hectares, 1/640 or 0.0015625 square miles. The acre is defined in square units because it is a measure of area and not length, and it can take any shape. A square measurement consists of a two-dimensional derivative of a linear measure, so a square foot refers to the area of a square with one-foot length sides.