Hey,
Initially for six months you are going to give breastmilk to your baby and in that case you would know how much milk to give to the baby as the baby will himself stop sucking milk or will stop latching once he is full. And if for some reason you will give him bottle feed then it is specified on the containers as how much milk one should make for the baby. Also, yes, you can ask your doctor also about the feeding.
You can also go through this link to get a fair idea.
https://www.healthychildren.org/English/ages-stages/baby/feeding-nutrition/Pages/Amount-and-Schedule-of-Formula-Feedings.aspx