How many ounces should a 2 month (10 week) old eat?

How many oz on average should a 10 week old eat during a sitting? I am temporarily working from home and nurse my son when needed until my mother comes at 10 to take over so I can get some work done. Usually, she gives a bottle when she gets there or after a nap. He currently takes 3 oz per bottle. He will have anywhere from 1 to 3 bottles while she is there until 4-5 pm, depending on his naps. He sometimes will nurse in-between depending on his mood. Recently, it seems the 3 oz isn't enough and I'm thinking about upping him to 3.5 oz a bottle? Usually he won't calm down after the bottle and will nurse briefly like topping off. Any thoughts?