To find the area of a rectangle, multiply the length by the width. The formula is: , where is the area, is the length, is the width, and · means multiply. A square is a rectangle with 4 equal sides.To find the area of a square, multiply the length of one side by itself. The formula is: or, where A is the area, s is the length of a side, and · means multiply.Let's look at some examples of finding the area of rectangles.iven the length and width of a rectangle, we can find the area. Given the area and one dimension of a rectangle, we can find the other dimension. The formula for area of a rectangle is: where is the length and is the width.