How to calculate the area of the bottom of a cylinder when its side is square

When the side of the cylinder is square, then the height of the cylinder is equal to the circumference of the bottom of the cylinder. On the premise of knowing the height of the cylinder, the area of the bottom of the cylinder is s = H ^ 2 / 3.14/4. On the premise of knowing the area of the side of the cylinder, the area of the bottom of the cylinder is s = s side / 3.14/4