A 6-month-old baby typically weighs between 14 and 18 pounds, depending on sex, birth weight, and feeding method. Boys tend to be slightly heavier, averaging around 17.5 pounds, while girls average closer to 16 pounds. But the range of “normal” is wide, and a single number on the scale matters far less than your baby’s growth pattern over time.
Average Weight at 6 Months
The World Health Organization growth charts, which pediatricians use as the standard reference, place the 50th percentile for 6-month-old boys at roughly 17.4 pounds (7.9 kg) and for girls at about 16 pounds (7.3 kg). The 50th percentile simply means half of healthy babies weigh more and half weigh less. It is not a target.
A baby tracking along the 15th percentile who has been there consistently since birth is growing perfectly well. A baby who was at the 75th percentile and has dropped to the 25th over two or three visits is more noteworthy, even though the 25th percentile is technically “normal.” What matters is the trajectory, not any single weigh-in.
The Birth Weight Rule of Thumb
Most babies double their birth weight by around 4 to 5 months of age. By 6 months, many have already passed that milestone. So if your baby was born at 7.5 pounds, you’d generally expect them to be in the ballpark of 15 pounds or more by now. Babies born smaller or larger will scale accordingly. A baby born at 6 pounds might weigh around 12 to 13 pounds at 6 months and still be perfectly on track.
How Fast Weight Gain Changes
Weight gain is not steady throughout infancy. It slows down as babies get older and more active. Between months 5 and 6, most babies gain about 4 to 5 ounces per week. After 6 months, that pace typically drops to 2 to 4 ounces per week. This slowdown is completely normal and often coincides with babies becoming more mobile, rolling, sitting up, and eventually crawling, all of which burn more calories.
Parents who track weekly weight sometimes worry when gains seem to flatten out around this age. That deceleration is expected. It does not mean your baby isn’t getting enough to eat.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies follow slightly different growth curves, and understanding the difference can save unnecessary worry. Healthy breastfed infants typically put on weight more slowly than formula-fed infants during the first year. Formula-fed babies tend to gain weight more quickly after about 3 months of age, and this gap persists even after solid foods are introduced.
This means a breastfed baby who weighs a pound or two less than a formula-fed baby of the same age is not behind. The WHO growth charts were designed using data from breastfed infants specifically, so they reflect this pattern. If your pediatrician is using the CDC charts instead (which are based on a mix of feeding types), a breastfed baby may appear to be gaining more slowly than expected even when growth is perfectly healthy.
When Weight Actually Signals a Problem
Pediatricians look for patterns, not snapshots. A baby who steadily falls off their expected weight curve over multiple visits may be evaluated for what’s clinically called failure to thrive. This isn’t diagnosed from a single weigh-in. It requires tracking weight measurements over time and seeing a persistent downward trend across percentile lines.
Some practical signs that your baby is getting enough nutrition at 6 months include producing at least six wet diapers per day, having regular bowel movements, and being alert and active during wakeful periods. Fewer than six wet diapers in 24 hours can be an early sign of dehydration or inadequate intake.
Sudden weight loss, refusing to eat for extended periods, or visible lethargy are more urgent signals than simply being on the lighter end of the growth chart.
Premature Babies and Corrected Age
If your baby was born early, their weight at 6 calendar months may look quite different from a full-term baby’s. Pediatricians use “corrected age” to account for prematurity, subtracting the number of weeks your baby arrived 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 is typically used until age 2. Premature infants may also be tracked on specialized growth charts designed for preterm babies until they reach their original due date, at which point standard charts apply. So if your preemie seems small compared to other 6-month-olds, the comparison itself may be misleading. Their corrected age is the better benchmark.
What Influences Your Baby’s Weight
Genetics play a significant role. Tall, larger-framed parents tend to have bigger babies, and smaller parents often have smaller ones. Your baby’s birth weight sets the starting point, and most babies settle into a percentile range within the first few months that reflects their genetic blueprint rather than their nutrition.
Illness can temporarily slow weight gain. A stomach bug, a cold that makes feeding uncomfortable, or a round of teething (which often ramps up right around 6 months) can all cause a brief plateau or even a small dip. These short-term fluctuations usually resolve on their own as appetite returns. A baby who bounces back to their growth curve within a week or two after being sick is following a normal pattern.
The introduction of solid foods, which most families begin around 6 months, can also affect the scale in either direction. Some babies take to solids quickly and gain a bit faster. Others are slow to warm up and continue getting most of their calories from breast milk or formula for several more weeks. Both paths are typical.