It'll fit two females fine but if you have larger males you'll want to get something a little bigger. I had this for my first two boys but when the got bigger I built a larger cage with room for more rats than just them. I also took the wheel out, my boys never used it (lazy bums) and it just took up space.

 

It's rather narrow for boys if it's anything but a temporary cage. For the same price (or maybe it's $10 more, I don't remember what I paid for that cage), you could get a rabbit cage by the same company that you could put hardware cloth (if the bar spacing is too big) over it and it should be pleanty big!

This is similar to what I have for my rabbit, but it has a wire door and is green:
http://www.petco.com/product/10638/Super-Pet-Extra-Large-My-First-Home.aspx

This is one not by the same company, but I like the look of it:
http://www.petco.com/product/13394/Marchioro-Small-Animal-Cage.aspx

This one is more expensive, but seems to be nice and is bigger.
http://www.petco.com/product/3294/Super-Pet-Deluxe-3-Story-Ferret-or-Rabbit-or-Chinchilla-Home.aspx

 

This one is more expensive, but seems to be nice and is bigger.
http://www.petco.com/product/3294/Super-Pet-Deluxe-3-Story-Ferret-or-Rabbit-or-Chinchilla-Home.aspx

I like this one best- you would have to add levels to the other two cages :wink:

 

Its a little bit on the small side if you get males, pay a little extra and get a bigger one, rats love climbing and lots of space to run around

 

I have that as a qt/sickie cage. I find it small for even two females, as it's pretty narrow. it would be a great cage it is was 18" deep instead!

This is how I had it set up when it was a QT cage for two 6 week old girls.