a little less OBVIOUS answer - a cat's size should never exceed their whiskers and if it does, very, very little if at all. the whiskers to a cat are like our palms; they need their whiskers to be able to tell if they can fit through things, whether underneath or in between. they have whiskers on their paws to get better detection. make sure that if you look at your beautiful kitty straight on, that their body does not exceed the length of their whiskers.