[PurpleKat]

I have just measured my hamster's bin cage from wilkos, xmas tree box

Her bedding depth is 8inches, due to the tapering (larger at top) I started on the top of her bedding.
It is 38 inches by 14 inches totalling 532 inches squared.

If you did lower bedding height then the dimensions will be smaller.
8 inches workes well as they can burrow deep but also with houses and other items they can't escape out the top.