450 is in fact the minimum in the US,but I think another good standard to go by is more species dependent.In theory a robo hamster in a 20 long to a 40 gallon tank would be about equal to a 6 inch long Syrian in a 1,550 square inch cage.
The main reason I know about the whole 450 square inch change is because I was,in fact,involved in that whole disaster before certain things happened.I won't go into detail,but I can say that it was all done for a very good reason and the size difference is for the sake of hamsters even if we should still be doing even better than this minimum
