At 5 months old, most babies weigh between 12 and 17 pounds and measure about 24 to 27 inches long. Boys tend to be slightly heavier and longer than girls at this age. These ranges cover the middle percentiles on standard growth charts, so healthy babies can fall above or below depending on genetics, feeding, and birth size.
Average Weight and Length at 5 Months
Based on World Health Organization growth standards (the charts recommended for all U.S. infants up to age 2), the 50th percentile for a 5-month-old boy is roughly 16.1 pounds and 25.9 inches. For girls, the 50th percentile is about 14.8 pounds and 25.2 inches. The 50th percentile simply means half of babies that age are bigger and half are smaller.
What matters more than hitting an exact number is where your baby falls on their own growth curve over time. A baby tracking along the 25th percentile at every checkup is growing perfectly well. Pediatricians pay closer attention when a baby jumps sharply between percentile lines, either up or down, than to where exactly on the chart they sit.
How Fast Babies Grow at This Age
Between 4 and 6 months, babies typically gain 1 to 1¼ pounds per month and grow about ½ to 1 inch in length each month. That pace is noticeably slower than the first three months of life, when weight gain can be twice as fast. By 5 months, most babies have at least doubled their birth weight, and many are close to it if they haven’t quite reached that milestone yet.
Head circumference also increases, though more gradually. Your baby’s head is growing to accommodate rapid brain development, and your pediatrician measures it at every well visit to make sure it’s tracking consistently.
Breastfed vs. Formula-Fed Differences
Breastfed and formula-fed babies don’t grow at exactly the same rate. 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 difference continues even after solid foods are introduced.
This is one reason the CDC recommends using WHO growth charts for all children under 2. The WHO charts are based on breastfed infants as the standard for normal growth, while older CDC charts reflected how American babies (predominantly formula-fed) actually grew during a specific time period. If your breastfed baby looks “smaller” compared to a formula-fed friend the same age, that’s a normal pattern, not a concern.
What Else Changes at 5 Months
Size isn’t just about weight and length. At 5 months, your baby’s body proportions are shifting. Their trunk is getting sturdier, which is why many babies start sitting with support around this time. Their legs are filling out with fat and muscle that will eventually power crawling and walking. You may notice your baby’s clothing size doesn’t match their age label perfectly, especially in length versus width. That’s normal.
Stomach capacity at this age is about 6 to 7 ounces, up from roughly 1 to 2 ounces as a newborn. Most 5-month-olds take in 24 to 36 ounces of breast milk or formula per day, spread across 4 to 6 feedings. Some parents begin introducing solid foods around this time, though many pediatricians recommend waiting until closer to 6 months when babies show clear readiness signs like sitting with minimal support and showing interest in food.
When Size Falls Outside the Range
Babies come in a wide range of healthy sizes. Genetics play the largest role: tall parents tend to have longer babies, and smaller parents tend to have smaller babies. Premature babies often track below standard percentiles for months or even years, since their growth timeline started earlier than expected. Doctors use “adjusted age” for preemies, meaning they compare your baby’s size to where they’d be based on their original due date rather than their actual birth date.
A baby consistently at the 5th percentile who is alert, feeding well, meeting developmental milestones, and producing plenty of wet diapers is generally healthy. The numbers that raise concern are sudden drops, like falling from the 60th percentile to the 15th over a couple of months, or a baby who stops gaining weight entirely. Your pediatrician tracks this pattern across multiple visits, which is why keeping those well-baby appointments matters even when your child seems perfectly fine.