A 20-day-old baby who is exclusively artificially fed needs about 500-800ml of milk per day. The amount of milk needed per day for artificially fed newborns varies greatly due to differences in physical condition and weight at birth. For a 20-day-old baby, the amount of milk needed is about 60-100ml per nursing session, and about 500-800ml per day every 3 hours. breastfed or mixed-feeding newborns are unable to calculate the exact amount of milk. Advocating newborns to breastfeed on demand, newborns usually sleep well, steady weight gain, newborns urinate more than 5~6 times a day, defecate 2~4 times a day, and when the newborn automatically stops sucking during breastfeeding, most of them indicate that the milk quantity is sufficient. Newborns should not be overfed, which can easily cause indigestion and spitting up. There is a big difference in feeding newborns, and when abnormalities such as lack of weight gain occur, you should consult a doctor in time and give appropriate adjustments under the guidance of a professional doctor.