4" should be good, could always stick some bricks under legs to raise it up a couple inches.The brooder has wooden legs. I guess it really isn't a problem to make it adjustable. Right now it has a 4" gap to get under it. Never had to adjust it with my previous chicks. How much would cornish x need to fit under there?
Now that I thing about it since they are fatter, less chicks will physically fit under it. So how many cornish x would fit if I usually fit 20 chicks?