A hyper cube with sidelength 1 has a 'volume' of 1. Then you sorta just define 'volume' (or the proper term 'hypervolume' based on how many hyper cubes you can fit. If the fit isn't perfect, half the size of your cubes, and try again. Whatever limit this system approaches is the true volume. (Edge cases are fractals, and they are already complicated in 3 dimensions)