A typical 6-month-old baby weighs around 16.1 pounds (7.3 kg) for girls and 17.5 pounds (7.9 kg) for boys, based on the World Health Organization growth standards. Most healthy babies fall somewhere between 13 and 21 pounds at this age, and a wide range is perfectly normal. The more useful number is often not the weight itself but where your baby sits on a growth chart and whether they’re following a consistent curve over time.
Average Weight at 6 Months
The WHO growth charts, which the American Academy of Pediatrics recommends for all infants through age 2, place the 50th percentile for a 6-month-old girl at about 16.1 pounds and for a boy at about 17.5 pounds. The 50th percentile simply means half of healthy babies weigh more and half weigh less. A baby at the 25th percentile is just as healthy as one at the 75th percentile, as long as they’re growing at a steady pace.
Here’s a rough breakdown by percentile for 6-month-olds:
- 5th percentile: About 13.5 lbs (girls) / 14.5 lbs (boys)
- 25th percentile: About 15 lbs (girls) / 16.2 lbs (boys)
- 50th percentile: About 16.1 lbs (girls) / 17.5 lbs (boys)
- 75th percentile: About 17.4 lbs (girls) / 18.8 lbs (boys)
- 95th percentile: About 19.4 lbs (girls) / 20.7 lbs (boys)
The “Double Your Birth Weight” Rule
A common benchmark pediatricians use is that a baby should roughly double their birth weight by 6 months. So a baby born at 7.5 pounds would be expected to weigh around 15 pounds. This isn’t a rigid target. It’s a quick gut check that growth is on track. Babies who were born smaller or larger will naturally land at different numbers, and the doubling timeline can vary by a few weeks in either direction.
How Weight Gain Slows Over Time
Babies don’t gain weight at a constant rate. In the first few months, infants typically gain about 1 ounce (28 grams) per day. Around 4 months, that slows to about 20 grams a day. By the time they reach 6 months, many babies are gaining 10 grams or less per day. This slowdown is completely normal and reflects a natural shift as babies become more active, start rolling, and prepare to sit up and eventually crawl. Parents sometimes worry when the numbers on the scale don’t climb as quickly as before, but a gradual deceleration is expected.
Breastfed vs. Formula-Fed Babies
How a baby is fed can influence their weight at 6 months. Exclusively breastfed babies who nurse directly tend to be slightly leaner than formula-fed babies. Research shows that infants who are partially breastfed (receiving both breast milk and formula) or exclusively formula-fed tend to have higher body mass relative to their length. Even among breastfed babies, those who occasionally receive expressed milk from a bottle tend to weigh a bit more than those who only nurse directly.
One reason for this difference is that bottle feeding, regardless of what’s in the bottle, can make it harder for babies to self-regulate how much they eat. When nursing directly, a baby controls the pace and stops when full. With a bottle, caregivers sometimes encourage finishing a set amount rather than watching for signs the baby has had enough. None of this means one method is wrong. It just explains why two healthy 6-month-olds can weigh noticeably different amounts depending on how they’re fed.
When Weight Falls Outside the Range
Pediatricians look for two main red flags on the growth chart. The first is a weight that falls below the 5th percentile for age and sex. The second, and often more concerning, is a drop across two or more major percentile lines over time. For example, a baby who was tracking at the 50th percentile and then falls to the 10th percentile would warrant a closer look, even if their actual weight still seems reasonable.
This pattern of falling off a growth curve is sometimes called “failure to thrive,” though the term is less about a diagnosis and more about a signal to investigate. Common causes include feeding difficulties, food allergies, reflux, or simply not getting enough calories. In most cases, the issue is identifiable and fixable. A baby who has always tracked along the 10th percentile and continues to do so is typically not a concern, even though they weigh less than average.
Premature Babies Need Adjusted Age
If your baby was born prematurely, the number on the growth chart needs context. Pediatricians use “corrected age” to plot growth for preemies, which means subtracting the weeks of prematurity from the baby’s actual age. A baby born 8 weeks early who is now 6 months old would be plotted on the growth chart as a 4-month-old. This adjustment continues until age 2, because premature babies need that extra time to catch up. Growth charts designed specifically for premature infants are also used during the earliest months before a baby reaches their original due date.
Starting Solids and Weight
Six months is also when most babies begin eating solid foods, which can influence weight in both directions. Breast milk or formula remains the primary source of calories at this age, with solid foods serving more as practice for eating than as a major nutritional source. Some babies take to solids quickly and gain a bit more, while others show little interest and continue getting nearly all their nutrition from milk. Both patterns are normal in the early weeks of introducing food.
Research has found that the transition to solids is tricky to get right calorically. Simulation studies suggest that following various complementary feeding guidelines while also breastfeeding can lead to either excess or insufficient calorie intake between 7 and 12 months, depending on how much breast milk the baby continues to drink. The practical takeaway: let your baby’s hunger and fullness cues guide portion sizes rather than trying to hit a specific amount of solid food each day.
Signs Your Baby Is Getting Enough
Between weigh-ins at the pediatrician, a few everyday signs tell you your baby is eating well. At least six wet diapers a day is a reliable indicator of adequate hydration and intake. Fewer than six wet diapers can be an early sign of dehydration. Beyond diapers, a baby who is alert, meeting developmental milestones, and steadily outgrowing clothes is almost certainly growing fine, even if their exact weight doesn’t match the average.
Growth is best measured over weeks and months, not day to day. A single weigh-in that seems high or low matters far less than the overall trend line. Your baby’s pediatrician tracks that trend at each well-child visit, and the pattern over time tells a much clearer story than any single number on the scale.