The average 6-month-old boy weighs about 17.5 pounds (7.9 kg), and the average 6-month-old girl weighs about 16.1 pounds (7.3 kg). But “average” is just the midpoint on the growth chart. A healthy 6-month-old can weigh anywhere from about 13 to 21 pounds, depending on sex, genetics, and feeding patterns. What matters most is not a single number but whether your baby is growing steadily along their own curve.
Average Weight by Sex
The World Health Organization growth charts, which pediatricians in the U.S. use for children under 2, place the 50th percentile for 6-month-olds at roughly 17.5 pounds for boys and 16.1 pounds for girls. The 50th percentile simply means half of babies weigh more and half weigh less. It is not a target.
Here’s a broader look at the range:
- Boys at 6 months: 5th percentile is about 14.1 lbs; 50th is about 17.5 lbs; 95th is about 21.2 lbs
- Girls at 6 months: 5th percentile is about 12.9 lbs; 50th is about 16.1 lbs; 95th is about 19.8 lbs
A baby tracking along the 15th percentile from birth is growing exactly as expected, even though they weigh less than most babies their age. A baby who has always been at the 85th percentile is also perfectly normal. Problems arise when a baby’s weight drops across two or more major percentile lines over time, not when they sit at a particular spot on the chart.
The Birth Weight Connection
Most babies double their birth weight by around 4 to 5 months of age. If your baby was born at 7 pounds, you’d generally expect them to be somewhere around 14 pounds by that point. By 6 months, weight gain has slowed noticeably. In the early months, babies gain about 1 ounce (28 grams) per day. By 4 months that slows to roughly 20 grams a day, and by 6 months many babies are gaining 10 grams or less per day. That tapering is completely normal and reflects the shift from rapid newborn growth to a more gradual pace.
Because of this pattern, your baby’s birth weight is one of the strongest predictors of where they’ll land at 6 months. A baby born at 6 pounds will typically weigh less at 6 months than one born at 9 pounds, and both can be perfectly healthy.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies grow differently, and this can cause unnecessary worry if you’re comparing your breastfed baby to a formula-fed peer. Breastfed infants typically put on weight more slowly than formula-fed infants during the first year. The gap tends to widen after about 3 months, with formula-fed babies gaining weight more quickly from that point on. This difference persists even after solid foods are introduced around 6 months.
Importantly, the difference is in weight, not length. Both groups grow in height at similar rates. The CDC recommends using WHO growth charts for all children under 2 specifically because those charts are based on breastfed infants and reflect optimal growth patterns. If your pediatrician is using these charts, a breastfed baby tracking along a lower percentile is being measured against the right standard.
What the Growth Chart Actually Tells You
Pediatricians look at growth charts the way you might look at a stock chart. A single data point tells you almost nothing. The trend over weeks and months is what matters. A healthy baby follows a relatively consistent curve, even if that curve runs along the 10th or 90th percentile. Small fluctuations between visits are expected, especially around growth spurts or illnesses.
The red flag is a sustained downward trend. Children’s Hospital of Philadelphia defines failure to thrive as physical growth that falls below the 3rd or 5th percentile, or a downward shift that crosses two major percentile lines. For example, a baby who was at the 50th percentile at 2 months and drops to the 10th percentile by 6 months would warrant investigation. That kind of drop could signal feeding difficulties, a food sensitivity, or an underlying medical issue. A baby who has always tracked at the 10th percentile, on the other hand, is likely just small.
Premature Babies Need Adjusted Calculations
If your baby was born early, their weight expectations at 6 months of calendar age are different from those of a full-term baby. Pediatricians use “corrected age” to account for prematurity. This means subtracting the number of weeks your baby was born early from their actual age. A baby born 8 weeks premature who is now 6 months old would be evaluated as a 4-month-old on the growth chart.
This correction continues until age 2. Premature infants often have their own specialized growth charts for the early months, then transition to standard WHO charts once they reach their original due date. If your baby was premature and you’re checking their weight against general 6-month milestones, the numbers will likely seem low. That gap typically narrows over the first two years as catch-up growth occurs.
Signs Your Baby’s Weight Is on Track
Beyond the number on the scale, several everyday cues suggest your 6-month-old is growing well. They should be producing at least 6 wet diapers a day, seem satisfied after feedings, and have good energy for their developmental stage (reaching for things, rolling, babbling). Their skin should bounce back when gently pinched rather than staying tented, which would suggest dehydration.
At 6 months, most babies are also starting solid foods, which can temporarily change weight gain patterns. Some babies slow down slightly as they learn to eat purees, while others pick up speed with the extra calories. Neither pattern is concerning on its own. The transition to solids is messy and gradual, and breast milk or formula still provides the majority of calories at this age.
If your baby’s weight has been steady on their growth curve, they’re feeding well, and they’re hitting developmental milestones, the specific number of pounds matters far less than the overall picture.