I use 18-20 depending on size, I suppose if I threw 4 huge ones in at a time I could cut down on the number of splits, but I'd be burning the same amount of wood.I never counted splits a day. I try to split mine 4 or 5 inch and 16 or 17 inches long.
I'll guess a cold Saturday or Sunday I use 15. I'm going to count tomorrow got me wondering now.