Your baby gets important nutrients from your breastmilk. In most circumstances, it is not necessary to actually measure how much milk your baby drinks, because usually babies suck as much as they want directly from the breast. All you need to do is count the number of times your baby passes urine on 24hrs and monitor weight gain. A baby that's getting adequate amount of breastmilk will pass urine at least 6 times in 24hrs. By calculation, your baby will probably need around 500ml of milk totally in a day.