How many ounces of breastmilk should my baby be eating at one month?

Enough to gain. Weight. If you are breast feeding then you do not know exactly...The baby will eat enough to be satisfied and gain weight. It will be 2-4 ounces a feed in general. If you are pumping, then it will be the same...2-4 ounces. (some bigger babies may be taking as much as 5-6 ounces). No worries if baby is growing. If not, then amount is more important and discussing with your doc is helpful.
Average 2-3 oz/feed. Research tells us that exclusively breastfed babies take in an average of 25 oz (750 ml) per day between the ages of 1 month and 6 months. Different babies take in different amounts of milk; a typical range of milk intakes is 19-30 oz per day (570-900 ml per day).