how much does your formula fed baby eat

My LO is 10 weeks old and formula fed. I know they are supposed to eat about 4 ounces ever 4 hours or so. He only eats 4 oz over night when he goes about 5 hours between feedings. He usually gets a bottle at 9:30pm and then wakes up around 2 or 3am to eat again. Throughout the day he wants to eat ever 2-3 hours and sometimes only eats 2oz at each feeding.