Good size for ferret cages?

[I love rats 2]

Hi I am doing research and thinking of buying 1 or 2 ferrets... But most importantly exactly how big should the dimentions of the cage be? Is there and ferret cage calculators out there?

[nakedrats]

The general rule I found is one ferret per full floor.  I keep my too-aggressive-for-cagemates single ferret in a R695 and she has a ton of room.  Another ferret wouldn't be too much, I think.  My judgement may be skewed because I got her when she was already 4 years old and she isn't terribly active. I like the 695 because the balconies allow for hanging cubes.  Get ferrets in multiples if possible.  Two isn't really harder to keep after than one.  If you do get one, go to a shelter and get one that is too dominant or too submissive to live with other ones.  I get mine out all the time and she lives with cats that she plays with and beats up mercilessly.  (the cats can easily get away from her on top of furniture if they want to, unlike another ferret)