I was browsing because it's fun seeing the cool habitrail kinda cages but... Really you should think about a 10 gallon fish tank with a mesh screen to cover it. I had two of these for my 7 mice for years. They never escaped (unlike these commercial cages, which I had a couple incidents with). As long as the mice have toys to climb around on and a wheel, you don't need this fancy plastic junk. They also sell water bottles that can be attached to the glass tanks really easily. So much easier to clean too! I never had to replace one either. Seriously, these types of cages are more like decoration than a habitat, i.e. they benefit humans interested in a fancy looking product more than the animals living inside But to answer your question, I'd put two mice in if you buy it.