Chicken nesting box sizes vary; one recommended size measures 9-inches high, 12-inches wide and 12-inches deep, with the entrance being 9-inches wide by 9-inches high. Chicken handlers adjust these dimensions for larger breeds.
Nest boxes must be large enough for the hens to lay and turn around comfortably, but not large enough for them to stand and roost. Boxes that allow for a lot of movement increase the risk of broken eggs. Straw, pine shavings or grass hay are used to line the chicken nesting boxes. However, cedar shavings pose a health risk because they are potentially toxic to the chickens.