Measure the length of one side of the square. It doesn't matter which side you use, since the sides of a square are all the same length.
Multiply the measurement by itself to find the area. For example, if one side of the square is 5 feet, the equation is 5 time 5 equals 25.
Express the answer in square units, such as square feet (ft2), square inches, square meters, square miles or square kilometers. In the example of a square with 5-foot sides, the area is 25 square feet.