A 3-week-old typically drinks 2 to 3 ounces of milk per feeding, eating 8 to 12 times over a 24-hour period. That works out to roughly 16 to 24 ounces total per day, though the exact amount varies based on your baby’s weight, whether they’re breastfed or formula-fed, and whether they’re in the middle of a growth spurt.
How Much Per Feeding
At 3 weeks, your baby falls right between the newborn and 1-month feeding ranges. Newborns start at 1 to 2 ounces per feeding, and by 1 month most babies take 3 to 4 ounces. A 3-week-old will land somewhere in the middle, typically finishing 2 to 3 ounces at a time. This makes sense physically: by day 10, a baby’s stomach has grown to about the size of a ping-pong ball, holding roughly 2 ounces. At 3 weeks, it’s only slightly larger.
A useful formula for estimating daily intake: babies need about 2.5 ounces of milk per pound of body weight per day. If your 3-week-old weighs 8 pounds, that’s about 20 ounces spread across the day. A 9-pound baby would need closer to 22 or 23 ounces. Regardless of your baby’s size, the upper limit is 32 ounces of formula in 24 hours.
Breastfed vs. Formula-Fed Babies
If you’re breastfeeding, you won’t know exactly how many ounces your baby takes per session, and that’s normal. Breastfed newborns may nurse for up to 20 minutes or longer on one or both breasts. As they get more efficient over the coming weeks, sessions will shorten to about 5 to 10 minutes per side. What matters more than timing each session is watching for fullness cues and tracking diapers (more on both below).
Breastfed babies tend to eat more frequently than formula-fed babies because breast milk digests faster. Expect feedings every 2 to 4 hours, which translates to 8 to 12 sessions in 24 hours. Some of those sessions will cluster together, especially in the evening. Formula-fed babies often go slightly longer between feedings, closer to every 3 to 4 hours, because formula takes longer to digest.
The 3-Week Growth Spurt
If your baby suddenly seems insatiable at 3 weeks, you’re likely in the middle of a growth spurt. Growth spurts commonly happen around 2 to 3 weeks, and they change feeding behavior noticeably. Your baby may want to nurse longer and more often, sometimes as frequently as every 30 minutes. They may also seem fussier than usual between feedings.
This is temporary, typically lasting 2 to 3 days. If you’re breastfeeding, the increased demand signals your body to produce more milk, so it’s important to feed on demand during this window rather than trying to stick to a schedule. Formula-fed babies may want an extra half-ounce to ounce per feeding during a growth spurt. Let your baby guide you.
How to Tell Your Baby Is Getting Enough
The most reliable daily indicator is diaper output. After the first 5 days of life, your baby should produce at least 6 wet diapers per day. The number of dirty diapers will vary, but breastfed babies at this age often have several per day. If you’re consistently seeing 6 or more wet diapers, your baby is almost certainly getting enough milk.
Steady weight gain is the other key measure. Your pediatrician will track this at well-baby visits. Most babies regain their birth weight by 2 weeks and then gain about 5 to 7 ounces per week through the first few months.
Reading Your Baby’s Hunger and Fullness Cues
Rather than watching the clock, watch your baby. Early hunger signs include putting hands to mouth, turning their head toward your breast or the bottle (called rooting), puckering or smacking their lips, and clenching their fists. Crying is actually a late hunger signal, so ideally you’d start a feeding before your baby reaches that point. A very upset baby can have trouble latching or settling into a feeding.
Fullness looks different: your baby will close their mouth, turn their head away from the breast or bottle, and visibly relax their hands. If your baby shows these signs but hasn’t finished the bottle, don’t push them to drain it. Babies are good at self-regulating intake when you follow their lead. Forcing extra milk can lead to overfeeding and spit-up, and over time it can override their natural fullness signals.
Signs Your Baby May Need More
A few patterns suggest your baby isn’t getting enough milk: fewer than 6 wet diapers in a day, dark-colored urine, persistent fussiness after feedings, or weight gain falling below expectations at a checkup. If your baby seems hungry again less than an hour after every feeding (outside of a growth spurt window), it may help to offer a slightly larger volume per feeding rather than increasing frequency alone.
For breastfeeding parents, low supply concerns are common at 3 weeks but actual low supply is less common than it feels. The best way to increase production is simply to nurse more often. If you’re supplementing with formula or unsure whether your baby is transferring milk well at the breast, a lactation consultant can do a weighted feed to measure exactly how much your baby takes during a nursing session.