A typical 6-month-old boy weighs around 17.5 pounds (7.9 kg), and a typical 6-month-old girl weighs around 16 pounds (7.3 kg). But “typical” covers a wide range. Healthy 6-month-olds can weigh anywhere from about 13 to 22 pounds, depending on their sex, genetics, birth weight, and how they’re fed. What matters most isn’t a single number on the scale but whether your baby is growing steadily along their own curve.
Average Weight by Sex
The World Health Organization growth standards, 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 pounds for girls. The 50th percentile simply means half of healthy babies weigh more and half weigh less. A baby at the 15th percentile is just as healthy as one at the 85th, as long as they’re following a consistent growth pattern.
Here’s a rough sense of the range at 6 months:
- Boys: 14.5 to 21 pounds covers roughly the 5th to 95th percentile
- Girls: 13 to 19.5 pounds covers roughly the 5th to 95th percentile
Weights below the 2nd percentile or above the 98th percentile are the thresholds the CDC flags as potentially abnormal. Even then, some babies are simply small or large because their parents are, and their pediatrician may not be concerned if everything else looks normal.
How Birth Weight Shapes the 6-Month Number
Most healthy, full-term newborns double their birth weight by about 4 months. By 6 months, many babies have surpassed that milestone and are on track to triple their birth weight by their first birthday. So if your baby was born at 7 pounds, you’d generally expect them to be well past 14 pounds by the half-year mark.
Between 4 and 6 months, infants typically gain about 1 to 1.25 pounds per month, according to Children’s Hospital of Philadelphia. That’s noticeably slower than the rapid gains of the first few months, and it’s completely normal. Growth naturally decelerates as babies get older, and many parents notice the change right around this age.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies don’t gain weight at the same pace, and the difference is well documented. After about 3 months, formula-fed infants typically gain weight more quickly. Breastfed infants tend to put on weight more slowly throughout the first year, and according to the CDC, this difference continues even after solid foods are introduced around 6 months.
This doesn’t mean breastfed babies are underfed. The WHO growth charts were built from data on predominantly breastfed infants, so a breastfed baby tracking along the 30th percentile is growing exactly as expected. Problems arise when parents or even some older growth charts treat the faster formula-fed pattern as the standard, which can lead to unnecessary worry or premature supplementation.
What Percentiles Actually Mean
Percentiles rank your baby against other babies of the same age and sex. A baby at the 25th percentile weighs more than 25% of babies and less than 75%. It’s a ranking, not a grade. A baby consistently tracking the 10th percentile is growing perfectly well. What draws a pediatrician’s attention is a baby who was cruising along the 60th percentile and drops to the 15th over a couple of visits, or one who jumps sharply upward. Crossing two or more major percentile lines in either direction usually triggers a closer look.
The CDC considers a weight-for-length below the 2nd percentile as low and above the 98th percentile as high. These are the outer boundaries where further evaluation is warranted. Between those extremes, the trajectory matters far more than the number itself.
Premature Babies Need Adjusted Age
If your baby was born early, the number on the scale at 6 months of actual age will likely look low compared to the charts. That’s why pediatricians use “corrected age” for preemies. You calculate it by subtracting the number of weeks your baby arrived early from their actual age. A baby born at 34 weeks (6 weeks early) who is now 6 months old would be compared against growth charts for a 4.5-month-old.
To find how many weeks early your baby was, subtract their gestational age at birth from 40 weeks. Most doctors continue using corrected age for growth tracking until the child is about 2 years old, at which point the difference between preemies and full-term babies has usually narrowed significantly.
Signs Growth Is on Track
Weight is one piece of a bigger picture. At 6 months, a baby who is growing well will also be gaining length, producing plenty of wet diapers (six or more a day), hitting motor milestones like rolling over and sitting with support, and showing interest in food. If your baby is alert, active, and developing new skills, a lower-percentile weight is rarely a concern on its own.
On the other hand, a baby who seems unusually sleepy, has very few wet diapers, or has visibly lost weight between checkups may need evaluation regardless of where they fall on the chart. Growth faltering, sometimes called failure to thrive, is typically identified by a pattern over time rather than a single weigh-in. That’s one reason the well-baby visits at 4 and 6 months are so useful: they give your pediatrician two data points to compare.
Getting an Accurate Weight at Home
If you’re curious between appointments, you can weigh your baby at home using an infant scale or the step-on-and-subtract method with a regular bathroom scale (weigh yourself holding the baby, then weigh yourself alone). Keep in mind that home scales are less precise, and a baby’s weight can fluctuate by several ounces depending on when they last ate or had a diaper change. For the most reliable tracking, use the weights recorded at your pediatrician’s office on the same calibrated scale each visit.