While some infants may be eating just 24 ounces a day, others may need 32 ounces or more. Rules of Formula Feeding A good rule of thumb is that the average baby at this age is likely to drink about 5 to 6 ounces of formula every 3 to 5 hours. The American Academy of Pediatrics, in the book Your Baby's First Year, also provides a nice guideline and suggests that 'on average, your baby should take in about 2 1/2 ounces of formula a day for every pound of body weight.'