How much (ml) breast milk should a 5 day old baby drink?

Measured how ?: A 5 do BF baby will take whatever is there.I know of no way to measure that accurately. If you are interested in the babies stomach capacity it approximates 60 ml/kg of the kids body weight. If the kid feeds actively,pees at least every 6 hrs, has alert periods alternating with naps & seems to be filling out I don't worry about volume of feeds.

About 5ml: Congratulations on the birth of your newborn. On average their stomach has a capacity of about 7ml but given that it is not totally empty, about 5ml of feed every 2-3 or 3-4 hours should be fine. Most babies will let you know when they need to be fed but don't let the baby go past 4 hours before you feed again.