A die is a cube and its faces are numbered 1-6 so all cubes and cuboid have six faces. If the side of the cube has length a, then the surface area is 6a² square units, because the area of each is length times width=a×a=a².

If you hold a die with the “1” face towards you and count its edges there are 4. On the back side (6) there are another 4 edges, and when you join the back to the front you have 4 more edges so there are 12 edges altogether. The total edge length is therefore 12a units.

The volume is length times width times height. These three are all the same so we have a×a×a=a³ cubic units.