C.G.
We have a gate up in the room with the litter box (mostly to keep the dog out). I just measured it and it is 4 1/2 inches. Our cat only weighs 10 pounds and she has plenty of room to crawl under. We probably could have lowered it more since she is so small. We never had any problems with our son trying to crawl under the gate....I'm not sure if that is why the manufacter has restrictions.