A 6-month-old baby typically weighs between 14 and 18 pounds, with the average boy coming in around 17.5 pounds (7.9 kg) and the average girl around 16 pounds (7.3 kg). These figures come from the WHO growth standards, which the CDC and the American Academy of Pediatrics recommend for all U.S. children under age 2, whether breastfed or formula-fed.
That said, “average” covers a wide range. A healthy 6-month-old might weigh several pounds above or below those numbers depending on birth weight, genetics, and feeding patterns. What matters most is that your baby is following a consistent growth curve over time, not hitting one specific number on the scale.
Average Weight by Sex
Boys tend to be slightly heavier than girls at every age during infancy. At 6 months, the WHO growth charts place the 50th percentile (the true midpoint) at about 17.5 pounds for boys and about 16 pounds for girls. The normal range stretches from roughly the 5th to the 95th percentile. For boys, that means anywhere from about 14.5 to 21 pounds can fall within the expected range. For girls, it’s roughly 13.5 to 19.5 pounds.
Your pediatrician plots your baby’s weight on these percentile curves at each well-child visit. A baby who has been tracking along the 25th percentile since birth is growing exactly as expected, even though they weigh less than average. A sudden jump across two or more percentile lines in either direction is what typically raises questions.
How Babies Reach This Weight
Weight gain slows down significantly over the first six months. In the early weeks, babies gain about 1 ounce per day. By around 4 months, that drops to roughly two-thirds of an ounce daily. By the time they hit 6 months, many babies are gaining less than half an ounce a day. This slowdown is completely normal and reflects a natural shift in growth priorities as babies start developing motor skills and burning more energy.
Between 4 and 6 months, expect your baby to put on about 1 to 1.25 pounds per month and grow roughly half an inch to three-quarters of an inch in length. That combination of weight and length gain is why your baby may look leaner at 6 months than they did at 3 months, even though they’re heavier.
The Birth Weight Benchmark
One of the simplest ways to gauge whether your baby’s growth is on track: most healthy, full-term babies double their birth weight by about 4 months and triple it by their first birthday. If your baby was born at 7 pounds, you’d expect them to be somewhere around 14 pounds by 4 months and closing in on 21 pounds near their first birthday. At 6 months, they’ll generally be somewhere between those two milestones.
Premature babies and those with a very low or very high birth weight often follow different timelines. Preemies may take longer to double their birth weight because their “corrected age” (adjusting for how early they arrived) is used to assess their growth.
Breastfed vs. Formula-Fed Babies
Feeding method has a real effect on weight patterns. Breastfed babies typically gain weight more slowly than formula-fed babies during the first year, and these differences become noticeable after about 3 months. A breastfed baby who sits at the 40th percentile at 6 months may be growing perfectly well, even if a formula-fed baby of the same age is at the 60th.
These weight differences persist even after babies start eating solid foods. This is one reason the WHO growth standards (which are based primarily on breastfed infants) are now the recommended charts for all babies under 2. Older CDC charts were built from data that included a higher proportion of formula-fed babies, which could make a normally growing breastfed infant look underweight.
What Starting Solids Means for Weight
Six months is the age when most pediatricians recommend introducing solid foods. It’s natural to wonder whether this will cause a weight jump. In practice, solids contribute relatively few calories at first because babies are just learning to eat. Breast milk or formula still provides the majority of nutrition at this stage.
Interestingly, research from Johns Hopkins found that many popular infant feeding guides recommend solid food portions that could push babies toward overweight BMIs within just a few months of starting solids. In simulations modeling 1,000 infants, following the portion sizes in most published feeding guides moved average BMI above the 85th percentile (the overweight threshold) well before the first birthday. Even cutting breast milk intake in half didn’t fully offset the extra calories from solids in most scenarios. The takeaway: letting your baby set the pace with solids, rather than following a strict portion guide, helps keep weight gain in a healthy range.
Signs of Healthy Growth Beyond the Scale
Weight is just one piece of the picture. Your pediatrician also tracks length and head circumference to make sure your baby is growing proportionally. A baby who is long and lean may weigh less than average but be perfectly healthy, while a shorter baby may weigh more without any concern.
At 6 months, developmental milestones offer another window into overall health. Most babies at this age can roll from tummy to back, push up with straight arms during tummy time, and lean on their hands while sitting. They’re reaching for toys, putting things in their mouths to explore, and closing their lips to signal they’re done eating. Socially, they recognize familiar people, laugh, and make back-and-forth sounds with you. A baby hitting these milestones while following a steady growth curve is thriving, regardless of where they fall on the weight chart.
Wet and dirty diapers also serve as a practical day-to-day indicator. If your baby is producing regular wet diapers and having consistent bowel movements, they’re almost certainly getting enough nutrition, even if their weight gain seems slow on paper.