The 2.5 ounces per pound rule
The American Academy of Pediatrics gives parents a simple starting point for formula: about 2.5 fluid ounces per pound of body weight over 24 hours. An 11-pound baby therefore needs roughly 11 x 2.5 = 27.5 ounces a day. Spread over the six or seven bottles a two-month-old typically takes, that is about 4 ounces per feeding, which lines up neatly with the standard feeding chart.
The rule has a ceiling. Most babies should not take more than about 32 ounces of formula in a day, so once a baby passes roughly 13 pounds the calculation flattens out and further growth is supported by richer feeding rather than more volume. If your baby seems hungry past 32 ounces, that is a conversation with your pediatrician about starting solids or checking the feeding routine, not a reason to keep adding bottles.
What a day of feeding looks like by age
Newborns in the first month take small, frequent feeds: 1 to 2 ounces at a time, 8 to 12 times in 24 hours, including overnight. Around one month the bottles grow to 3 or 4 ounces and drop to 7 or 8 a day. By two to three months most babies take 4 to 5 ounces, six or seven times daily, and start stretching the overnight gap. From four to six months the bottles reach 6 to 8 ounces, five or six times a day.
Between 6 and 12 months formula stays the main source of nutrition but solids begin to share the load. Most babies in that stretch drink 24 to 32 ounces a day across four or five bottles plus two or three small meals. Whole cow's milk replaces formula at the first birthday, not before; water in small amounts can be offered with meals from about six months.
Feed on demand, and watch the baby rather than the bottle
Every number here is an average, and averages do not apply neatly to one infant on one day. Intake swings with growth spurts, teething, illness and sleep. The reliable signals are steady weight gain along the pediatrician's growth curve, six or more wet diapers a day after the first week, and a baby who settles after feeding. Hunger cues, rooting, bringing hands to the mouth, smacking lips and fussing, come before crying; crying is a late sign.
Never force a baby to finish a bottle, and never add extra water to stretch formula, which dilutes the sodium and can cause seizures. Mix exactly as the label directs. Prepared formula keeps for one hour at room temperature once a baby has fed from it and 24 hours refrigerated if untouched. Premature babies, babies with reflux, cardiac conditions or poor weight gain follow feeding plans set by their care team, and those plans override any rule of thumb on this page.