My nest boxes are 12"x12"x12" and I've found three large dual purpose hens stuffed in there together. Chickens are mostly fluff, they compress down quite a bit and can fit in very small spaces. Now I'm thinking I should've made the boxes smaller, so they wouldn't fit more than one chicken, but I know the chickens would've still found a way to cram themselves in there by the multiples. When they have a favorite box, they REALLY have a favorite box!