The surface area of a cuboid is equal to twice the sum of length times width times height times width times height, or twice the length times width, twice the length times height, and twice the width times height.

The surface area of a cube is the area of six squares, that is, the side length multiplied by the side length multiplied by 6, the side length multiplied by the side length is the area of one face of the cube, and then multiplied by 6 is the area of six faces. Which is the surface area of the cube.