You are right, you do know the answer

Follow his lead..he will certainly let you know when he wants more. My DD is 2mths old and I don't really count her feeds just give it to her when she wants or convenient for me if she will take it. That's the beauty of demand feeding or baby lead feeding.
My DD actually laughs when I try to get her to take more and push the nipple away with her tongue..cheeky little monkey!