The 5 sided acrylic cube sizes listed are made with 3/16" thick acrylic. The measurements are outside dimensions.  Standard cubes are glued with square corners. We offer making these cubes with bent corners and we can make any custom size. They don’t need to be square; they can be a rectangle or a custom size.  When ordering custom sizes; order by inside dimensions. We can quote custom cubes and standard cubes in other material thickness also.