If you really mean the AREA of a cylinder, you must mean the Surface Area. For that, imagine cutting the cylinder (a can) downward and flattening it out. The surface area of the cylinder is area of the rectangle formed, whose height is the same as the height of the can, and whose length is the circumference of the can's top, or 2 x Pi x Radius.If you mean the VOLUME of a cylinder (a can), it's Pi x R squared x H.