Two things related to feedings happen to many babies at 3 months: they go through a growth spurt, and begin sleeping through the night without waking to eat.
While you might be able to skip that 3 a.m. feeding, your 3-month-old will drink more formula at each feeding. The exact amount of formula your baby needs depends largely on his weight.
Weight
As a general rule, a 3-month-old baby should eat 2.5 oz. of formula a day for every pound of body weight. In other words, multiple your baby’s weight in pounds by 2.5 oz. to get the total amount of ounces of formula for a 24-hour period. At the beginning of 3 months, babies generally take five to seven bottles of 4 to 6 oz. a day. At the end of 3 months, babies need an additional ounce of formula at each feeding, but may take one less bottle.
Signals
Look to your baby’s signals to decide how much to feed her.
Your 3-month-old will eat when she’s hungry and stop when she’s full. When your baby cries, and the reason is not a wet diaper or irritant, such as temperature or noise, hunger is the likely cause. Other signals include lip smacking, sucking, putting her hands to her mouth, and turning her head toward you when you stroke her cheek.
When your baby stops feeding, she is likely full. If you’ve finished the bottle, and your baby is still hungry, she may look around for more, and happily take another bottle when you offer it.
Underfeeding
Not gaining enough weight is often a sign of underfeeding. Up to 3 months, your baby should gain 1 oz. of weight every day. From 3 to 4 months, your baby should gain about 1/2 oz. a day.
If your baby cries with no clear reason or doesn’t have at least one wet diaper six hours, he may be underfed.
Physical signs of underfeeding include skin that appears loose or wrinkly, the soft spot –- or fontanel –- appearing sunk in, and a baby that acts listless and very tired. Contact your doctor if you’re concerned your baby is not eating enough.
Overfeeding
To prevent overfeeding, ensure the hole on the bottle’s nipple is the right size to let the formula slowly drip. If the hole is too big and the formula pours out, your baby is more likely to overfeed.
Signs of overfeeding include gaining more weight than your doctor says is appropriate, throwing up most of the formula immediately after drinking it, and belly pain right after a feeding. If your baby has belly pain, she may pull her legs up to her belly and cry. Talk to your doctor if you’re worried about overfeeding.