Is it for a Syrian or a dwarf hamster? The size is good - I can’t think in inches and square inches, more proportions - but 40” is about 100cm I think which is a good length. 20 inches is 50 cm so another 1.5” means it’s about 53cm deep which is also a good size - even though those are maximum sizes at the top. Height is about 45cm so will for a 12” wheel easily.
For a dwarf hamster it’s good. For a Syrian the depth (53cm but maybe more like 40cm lower down) isn’t as deep as ideally. But it’s a good length and if set up carefully it could be a good cage
