The average weight of a 6-month-old baby is about 7.6 kg (16.75 lbs) for boys and 7.0 kg (15.4 lbs) for girls. These numbers represent the 50th percentile on the WHO growth charts, meaning half of all healthy babies weigh more and half weigh less. But “average” is just one point on a wide spectrum of normal, and understanding where your baby falls on that spectrum matters more than hitting an exact number.
Normal Weight Ranges for Boys and Girls
There’s a significant spread between the lightest and heaviest healthy babies at six months. For boys, the normal range runs from about 6.6 kg (14.5 lbs) at the 5th percentile to 9.5 kg (20.9 lbs) at the 95th percentile. Girls tend to be slightly lighter across the board, with a range roughly half a kilogram lower at each end. A baby at the 10th percentile who has been tracking along that curve since birth is growing perfectly well. The number on the scale matters far less than whether the baby is following a consistent trajectory on their growth chart.
What Matters More Than the Number
Pediatricians don’t compare your baby to an average. They track your baby against themselves over time. A baby who was in the 25th percentile at two months and is still near the 25th percentile at six months is on a healthy, predictable growth path. The clinical concern arises when a baby’s weight crosses two or more percentile lines on their growth chart after previously growing on a steady curve. That kind of shift, not any single weight measurement, is what signals a potential problem worth investigating.
By six months, the pace of weight gain has slowed considerably from the early newborn period. Many babies are gaining about 10 grams or less per day at this age, compared to the much faster gains of the first few months. This slowdown is completely normal and catches some parents off guard, especially if they’ve gotten used to seeing rapid jumps on the scale.
Breastfed vs. Formula-Fed Babies
How a baby is fed influences their growth pattern in ways that can look alarming if you’re comparing to the wrong reference point. Breastfed babies typically gain weight more slowly than formula-fed babies during the first year, with the divergence becoming more noticeable after about three months of age. Formula-fed infants tend to put on weight faster from that point forward, and the difference in weight patterns persists even after both groups start eating solid foods.
This is one reason the CDC recommends using the WHO growth standards for all children under two, regardless of how they’re fed. The WHO charts were built from data on breastfed infants and reflect the biological norm for human growth. If your breastfed baby looks like they’re “falling behind” on an older chart designed around formula-fed babies, the chart may be the issue, not your baby.
Adjusted Weight for Premature Babies
If your baby was born early, the number on the calendar doesn’t tell the whole story. A baby born two months premature who is now six months old should be compared to growth expectations for a four-month-old. This is called corrected age, and pediatricians use it when plotting growth until a child turns two. Premature infants may also need specialized growth charts in their earliest months before transitioning to standard WHO charts once they reach their original due date.
How Starting Solids Affects Weight
Six months is also when most families begin introducing solid foods, which changes the growth equation. Research suggests that predominantly breastfeeding and waiting until after four months to introduce complementary foods is associated with lower odds of excessively rapid weight gain in the first year. This doesn’t mean solids cause unhealthy weight gain. It means the timing and balance of milk feeds plus solids can shape how quickly a baby’s weight climbs. At this stage, breast milk or formula still provides the majority of calories, and solids are more about learning to eat than meeting nutritional needs.
Most babies at six months are experimenting with purees or soft foods once or twice a day while continuing their usual milk feeds. The caloric contribution from solids at this point is small, so you’re unlikely to see a dramatic weight change in either direction just from starting a few spoonfuls of mashed sweet potato.
Signs of Healthy Growth at Six Months
Beyond the scale, a healthy six-month-old shows their growth in other ways. They’re typically doubling their birth weight by this age, which is a rough but useful benchmark. They’re gaining length steadily, and their head circumference is increasing on a predictable curve. They have good muscle tone, are reaching developmental milestones like sitting with support and reaching for objects, and they’re producing plenty of wet diapers throughout the day.
If your baby’s weight is well outside the typical range or has shifted dramatically from their established growth curve, that’s worth a conversation at your next well-child visit. But a single weigh-in that looks high or low compared to an online average is rarely meaningful on its own. Growth is a pattern, not a snapshot.