What formula is used to calculate the area of a square?

To calculate the area of a square, the appropriate formula is S², where S represents the length of one side of the square. Area is defined as the amount of space contained within a two-dimensional shape, and for a square, this is determined by multiplying the length of one side by itself. Since all sides of a square are equal, using the formula S times S gives the total area.

The other options mentioned do not represent area. For instance, 4S refers to the perimeter of the square, as it calculates the total length around the square by summing the lengths of all four sides. S + S simply sums the lengths of two sides, which does not apply to area calculations. Lastly, 2S denotes the length of two sides, which doesn't reflect the calculation of area either. Thus, S² is the only correct formula for determining the area of a square.