How much should a 6 week old baby eat?

Feed him/her on demand when hungry. The general guideline for feeding a newborn is for infants 0-3 weeks: 8-10 feedings daily of 2-3 oz / 60-100 ml per feeding; for infants 1-4 months: 6-8 feedings daily of 4-5 oz / 125-150 ml per feeding.