Heights between eight inches and 12 inches are usually the est. This prevents litter or waste from spilling over the sides, especially if your cat loves to bury her waste. However, there should be an entrance that is lower to the ground around five to six inches so your cat can comfortably enter and exit the litter box. Some litter boxes are open at the entrance while others have a flap door that completely encloses the litter box while your cat is using it. This is based on preference—both yours and your cat’s.