In common use a cylinder is taken to mean a finite section of a right circular cylinder, i.e., the cylinder with the generating lines perpendicular to the bases, with its ends closed to form two circular surfaces, as in the figure (right). If the cylinder has a radius r and length (height) h, its surface area is:
the area of the top (πr2) + the area of the bottom (πr2) + the area of the side (2πrh).