rule of thumb the bigger the better, and as much floor time that you could give that bunny. I have a dutch rabbit and she is in a c&c cage that is 2 grids wide, 3 grids long and two story hig, the second story is a shelf. I have a pen attatched and she gets out all day from about 8 am to about 9 pm so that size is fine, if i was to not be able to let her out all day i would defintely make the cage bigger. She is now sharing that cage with her husbun who is a lop, and i am not at this time making the cage bigger, but feel it is ok because they are allowed out all day long.