So, given those caveats, you may still be wondering how much formula in general your baby needs? As a rule of thumb, infants under six months who haven't yet started solids should be taking 2 to 2Â½ ounces of formula per pound of body weight over a 24-hour period. So, if your baby weighs 10 pounds, that would translate to 20 to 25 ounces of formula a day; in a 24-hour period you'll be feeding your baby about 3 to 4 ounces every four hours.