I use the large lab boxes for my mice. I keep up to 1.4 mice per tub and they do really well and seem to enjoy all the space. I think they are too small for rats though, just one or 2 mediums may be OK, but I can't imagine a large breeder male and his girls being comfortable in there.

Great price on the boxes though. I tried to get a few more for the mice, but he didn't want to ship.