A typical 5-month-old baby weighs around 14 to 16 pounds and measures about 25 to 26 inches long, though there’s a wide range of normal. Boys tend to run slightly heavier and longer than girls at this age. What matters more than hitting an exact number is whether your baby is growing steadily along their own curve over time.
Average Weight and Length at 5 Months
Based on the WHO growth standards used by pediatricians, the 50th percentile (the midpoint) for a 5-month-old boy is roughly 16.1 pounds and 26 inches long. For girls, it’s about 14.8 pounds and 25.2 inches. But “average” is just the middle of a bell curve. A baby at the 25th percentile is just as healthy as one at the 75th percentile, as long as they’re following a consistent trajectory on their growth chart.
Percentiles simply rank where your baby falls compared to other babies the same age. If your baby is at the 30th percentile for weight, that means 30% of babies weigh the same or less. Pediatricians watch for sudden jumps or drops across percentile lines, not the percentile number itself. A baby who has tracked along the 20th percentile since birth is growing perfectly normally.
How Fast Babies Grow at This Age
Between 4 and 6 months, babies gain about 1 to 1.25 pounds per month on average. That’s noticeably slower than the first few months of life, when weight gain is more rapid. Length increases by roughly half an inch to an inch per month during this window. Head circumference also continues to grow, typically about half an inch per month, reflecting ongoing brain development.
This is the age when growth rates start to diverge based on how a baby is fed. Breastfed babies typically put on weight more slowly than formula-fed babies after about 3 months of age. This is a normal pattern, not a sign of a problem. Formula-fed infants tend to gain weight more quickly through the rest of the first year. Pediatricians are aware of this difference and account for it when reviewing growth charts.
What About Premature Babies?
If your baby was born early, their growth should be measured against their corrected age, not their calendar age. To calculate corrected age, subtract the number of weeks your baby arrived early from their actual age. So a baby born at 32 weeks (8 weeks early) who is now 5 months old has a corrected age of about 3 months. Their size and development should be compared to a 3-month-old’s milestones, not a 5-month-old’s.
This adjustment matters for the first two years. A premature baby who looks small for 5 months may be perfectly on track for their corrected age. Growth charts should reflect this adjusted timeline, and most pediatric offices will track both ages during well-child visits.
Clothing and Diaper Sizes
Most 5-month-olds fit into 3-to-6-month or 6-month clothing, though longer or heavier babies may already be in 6-to-9-month sizes. Baby clothing sizing is notoriously inconsistent across brands, so weight and length are better guides than the age printed on the label.
For diapers, a baby in the 14-to-16-pound range typically wears a size 3, which fits babies from 16 to 28 pounds. Some smaller 5-month-olds may still be in a size 2 (12 to 18 pounds). Diaper sizing is based on weight, not age. Signs you need to size up include frequent leaks or blowouts, red marks on the thighs or waist, or a diaper that no longer fully covers your baby’s bottom. You should be able to fit two fingers comfortably under the waistband for a proper fit.
Physical Milestones at This Size
A 5-month-old’s growing body supports some exciting new abilities. Most babies this age are rolling over (or close to it) and kicking their arms and legs with more purpose. When placed on their stomach, they can lift their head and may push up on their arms. Some babies start bearing weight on their legs when held upright, though they’re still months away from standing on their own.
Hand coordination is improving too. Your baby is grasping objects, pulling things closer with a raking motion, and putting everything within reach straight into their mouth. Sitting independently comes closer to 6 months for most babies, but at 5 months many can sit briefly with support. These motor skills develop alongside physical growth, as stronger, heavier muscles give babies the power to move in new ways.
When Growth Patterns Shift
It’s common for babies to cross a percentile line or two in the first year, especially between 4 and 6 months as growth naturally slows from its newborn pace. A baby who was in the 60th percentile at 2 months and drops to the 45th percentile at 5 months is not necessarily falling behind. Small shifts are expected.
What pediatricians look for is a pattern of sustained decline across two or more major percentile lines, or a baby whose weight-for-length ratio is significantly out of proportion. Genetics plays a large role in size. Two smaller parents are likely to have a baby who tracks along lower percentiles, and that’s completely normal. The growth chart is a screening tool, not a report card.