I moved my mice who gave birth to 24 pinkies to the larger bin due to concerns of the babies becoming hoppers would jump out. since the bin 15" high x 14" W x 23" L, I figure to build mice apt building with 4 floors. Each floor has a 1/2" hole so they can travel up or down each floor. In case, they can also use the fire escape ladder, which one mouse already gave it a try. None of the mice moved in yet, but I figure once the babies are grown up. I make 3 more I should be able to triple the number of mice I can keep. Of course, it would be mostly female mice. Each floor is 3-4 inches in height. All containers were made from Lactaid milk containers.