Remember it the sq feet of a cube. Not the Sq Feet of a 2d surface.
Measure the length of one of the cube's edges.
Multiply this measurement by itself, which is called "squaring." For instance, if a cube has an edge that is 2 inches long, multiply 2 by 2 to get 4, meaning that the area of this face is 4 square inches.
Multiply your answer from step two by 6, since there are six faces on a cube. In this example, you would multiply 4 by 6 to get a total square footage of 24 inches