A 3-week-old baby will eat about every two hours. Depending on your baby's rate of growth, she may drink anywhere from 59.1 to 147ml of milk at a time. Doctors generally suggest that a baby drinks 56.7 to 85.1gr of formula per pound of weight per day. A 10 pound baby should get between 567 and 851gr of formula per day.
Millitres per kg
A 3-week-old baby will eat about every two hours. Depending on your baby's rate of growth, she may drink anywhere from 57 to 142 ml (2 to 5 ounces) of milk at a time. Doctors generally suggest that a baby drinks 150 ml per kg of body weight per day (or 2 to 3 ounces of formula per pound of weight per day). A 4 kg baby should get around 600 ml of formula or milk per day (or a 10 pound baby should get between 20 and 30 ounces per day).
Recognise the signs
At 3 weeks old a baby should be wetting as many as 10 to 12 nappies a day and having at least one bowel movement, although breastfed babies often have more. A baby who is getting enough milk will also gain weight consistently and be eager to eat.
According to the staff of the Mayo Clinic, you should "trust your instincts--and your newborn's. Parents often worry that their newborn isn't eating enough. But babies usually know just how much they need. Don't focus on how much, how often and how regularly your baby eats. Instead, look for contentment between feedings, alertness, good skin tone and steady weight gain--about 115 to 200 g (4 to 7 ounces) a week for the first month."