Average Baby Weight And Length: Month-By-Month Charts

The WHO has determined standards for infant growth in terms of average weight and length for age. Unlike the body mass index for adults, infant growth is evaluated by their height and weight at certain ages. The Centers of Disease Control and Prevention (CDC) recommends following these growth charts when monitoring the growth of a child in the first two years of life.

Most babies (80 out of every 100) born at 40 weeks of pregnancy, or full term, weigh between 5 pounds 11.5 ounces (2.6 kilograms) and 8 pounds 5.75 ounces (3.8 kilograms). This is considered a healthy average. Babies who weigh less are considered small, while babies who weigh more are considered large. However, this information can’t predict your child’s weight later in life^[1]Tracking Your Baby’s Weight and Measurements. Healthy Children. Accessed 9/7/2023. .

The average length for girls at birth is 19.2 inches (49.1 cm). The average length for boys at birth is 19.7 inches (50 cm)^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

Tracking your baby’s weight is an essential in monitoring their health. “A baby’s weight is a vital sign that gives us insight into their growth and development,” explains Mona Amin, D.O., a Fort Lauderdale, Florida-based board-certified pediatrician, Philips Avent partner and owner of Peds Doc Talk, an online parenting resource. “Extreme weight loss or weight gain can point to metabolic or endocrine conditions. And in the early months, weight is an important marker that feeding is going well,” she explains. Poor weight gain in the first few months of life can mean the baby is getting an insufficient calorie intake or dealing with reflux that needs treatment, says Dr. Amin.

When it comes to your baby’s weight, the most important factor is that your baby is continuing to gain weight and is staying on their growth curve, whether they are on the lower or higher end. “Your baby’s weight should be followed relative to him/her and not compared to other babies,” says Jenelle Ferry, M.D., a neonatologist and director of feeding, nutrition and infant development at Pediatrix Neonatology of Florida. “As a parent, it’s hard not to compare your baby to others, but growth and development are so different for every baby and there are pretty wide ranges of normal, so it’s important to make sure your baby is following their path and not someone else’s.”

It’s also important to note that when a baby is first born, they will lose weight immediately after birth, says Dr. Ferry. This is typical and expected, she explains, noting that a healthy baby receiving breast milk should return to their birth weight by two weeks old. “After that, they should continue to grow along their growth percentile,” she says.

Factors That Influence Baby’s Weight Gain

A baby’s weight is influenced by several factors, including:

• Pregnancy issues or conditions: “In the womb, there can be issues that affect blood flow in the placenta that may restrict the growth of a fetus,” says Dr. Ferry. Moms who have gestational diabetes may also birth larger babies and that can change their growth trajectory after birth, she adds.
• Baby’s birth weight: A baby’s weight at birth can determine their growth moving forward. “If a baby was large for gestational age, small for gestational age or growth restricted, and especially if there were placental factors during the uterine life that influenced growth positively or negatively, they may adjust percentiles either in infancy or toddlerhood to adjust more to their genetic potential,” Dr. Ferry explains. For example, Dr. Ferry explains, if a baby was born at the 90th percentile because mom had gestational diabetes, that growth in utero was affected by external factors to the baby and may not be quite their genetic potential. If they didn’t have those influences, it’s possible they would have been born at the 50th percentile. “In those cases, sometimes over the first year or two of life, they may readjust to a kind of genetic potential growth percentile. So a baby who was born large because of gestational diabetes may not always grow at the 90th percentile, but may drop to, say, the 75th percentile and then grow along that.”
• Calorie intake: How much food your baby is consuming, whether it’s breast milk or formula, will impact their weight, says Dr. Mona. “It is also impacted by overall nutrition and metabolism, which varies from baby to baby,” she adds.
• Genetics: The size of the parents can influence the baby’s weight at birth and moving forward. Bigger parents may have a bigger baby and smaller parents can expect their baby will be small, too.
• Gender: Girls tend to weigh a bit less than boys, however this is not a general rule, and the difference can be very small.
• Multiples: Being born as a multiple (like a twin or triplet) can also affect a baby’s weight because of placental factors, like if the placenta distributes nutrients differently to the multiples, leading to one being smaller than the other, or if both are smaller because of limited space or nutrients, Dr. Ferry explains. “Once outside of the womb, most multiples should continue growing regularly along a growth percentile. Any baby who has had intrauterine growth restriction may have more difficulty gaining weight after birth,” she says.

Average Baby Weight Chart by Month

The WHO growth chart for weight is meant for healthy, full-term infants. Take note that this chart reflects growth patterns among babies who predominantly consume breast milk for at least the first four months of life and up to the first year^[3]WHO Growth Standards Are Recommended for Use in the U.S. for Infants and Children 0 to 2 Years of Age. Centers of Disease Control and Prevention. Accessed 9/7/2023. . Breastfed babies typically gain weight more slowly than formula-fed babies in the first year of life.

Babies experience rapid growth and development in the first year of life. “Monitoring a baby’s weight is one of the ways to ensure they are thriving and growing,” says Dr. Ferry. “For a breastfed baby, monitoring the weight is a way to ensure they are getting enough milk.”

Average Baby Weight at 2 Months

At 2 months old, the average baby weight for boys is 12 pounds 5 ounces (5.6 kilograms)^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. . The average weight for girls at 2 months is 11 pounds 4 ounces (5.1 kilograms)^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. . In general, babies will gain about an ounce of weight each day during the first three months of life.

Average Baby Weight at 6 Months

From birth to 6 months old, babies should double their birth weight^[6]Baby Weight Gain: A Guide To Their First Year. Texas Children’s Hospital. Accessed 9/7/2023. . The average weight for boys at 6 months is 17 pounds 8 ounces (7.9 kilograms) and the average for girls is 16 pounds 2 ounces (7.3 kilograms)^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. ^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

Average Baby Weight at 12 Months

Babies should triple their birth weight by their first birthday^[6]Baby Weight Gain: A Guide To Their First Year. Texas Children’s Hospital. Accessed 9/7/2023. . The average weight for boys at 12 months is 21 pounds 3 ounces (9.6 kilograms) and the average weight for girls is 19 pounds 10 ounces (8.9 kilograms)^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. ^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

At each pediatrician well-visit, your baby’s length will be measured. Their length is measured from the top of the head to the heel of one foot.

“Growing appropriately for length, and especially maintaining their length and weight ratios, indicates good lean mass growth,” says Dr. Ferry. “This doesn’t mean we want babies to be skinny, but we do look for good healthy growth that indicates the organs, bones and muscles are growing, not just putting on weight from adipose (fatty) tissue.”

A baby’s length can be harder to accurately measure than weight, because babies generally don’t like to stay still. “Length is also a trend and can sometimes jump due to incorrect measurements (it’s hard to get a baby’s leg really straight), so we do look at the big picture,” says Dr. Mona. “If we see major errors or fluctuations, your clinician may remeasure to confirm and track accordingly.”

Factors That Influence Baby’s Length

Just like with weight, there are factors that can affect your baby’s length. These include the following:

• Genetics: In general, taller parents tend to have longer babies, while shorter parents have shorter babies. Of course, this is not a hard and fast rule.
• Nutrient intake during pregnancy: What a mother eats during pregnancy can contribute to both the birth weight and length of a baby.
• Conditions during pregnancy: Health issues that the mother may face when pregnant can also affect length. These can include gestational diabetes, maternal anemia or high blood pressure.
• Gender: Boys tend to be longer in length than girls.

Average Baby Length Chart by Month

The WHO growth chart is based on healthy, full-term infants who are predominantly breastfed in their first year of life^[3]WHO Growth Standards Are Recommended for Use in the U.S. for Infants and Children 0 to 2 Years of Age. Centers of Disease Control and Prevention. Accessed 9/7/2023. .

As your child gains weight, they will gain length as well. As Dr. Ferry notes, weight gain and length gain should continue in a healthy ratio.

Average Baby Length at 2 Months

At 2 months, the average baby girl will measure 22 ⅕ inches (57.1 centimeters)^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. . The average baby boy will measure at 23 inches (58.4 centimeters)^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

Average Baby Length at 6 Months

You can expect babies to gain about one inch per month in the first 6 months of life^[6]Baby Weight Gain: A Guide To Their First Year. Texas Children’s Hospital. Accessed 9/7/2023. . At 6 months, the average baby girl will measure at 25.75 inches (65.7 centimeters) and the average baby boy will be 26.5 inches (67.6 centimeters)^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. ^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

Average Baby Length at 12 Months

Between 6 months and 12 months, babies generally won’t add quite as much length and will usually gain about half an inch per month^[6]Baby Weight Gain: A Guide To Their First Year. Texas Children’s Hospital. Accessed 9/7/2023. . At 12 months, the average baby girl will measure at 29 inches (74 centimeters) and the average baby boy will be 29.75 inches (75.7 centimeters)^[4]Data Table for Girls Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. ^[2]Data Table for Boys Length-for-age and Weight-for-age Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

The WHO growth chart is the standard when it comes to monitoring a baby’s growth, but it’s important to know what it means so it doesn’t cause unnecessary concern.

Remember that the WHO growth chart is based on full-term, predominantly breastfed babies, as healthy breastfed infants are considered the standard. While formula-fed babies can gain weight faster than breastfed babies in the first year of life, the CDC notes that both breastfed and formula-fed babies follow a similar pattern in terms of linear growth^[7]Growth Chart Training: Using the WHO Growth Charts. Centers for Disease Control and Prevention. Accessed 9/7/2023. .

When reading growth charts, it’s more important to pay attention to whether or not your baby is consistently gaining weight and length rather than the exact number of pounds or inches they’re putting on. “Remember that a growth chart is just an average of all baby weight ranges,” says Dr. Ferry. “It’s not like passing a test, where 10% is failing. Ten percent of all normal babies will be at the 10th percentile.”

It may be cause for concern if your baby, who has always been on or around the 50th percentile, suddenly drops to the 10th percentile. “This could be a cause for close monitoring or concern,” says Dr. Mona. “Large fluctuations from visit to visit may point to underlying medical concerns we need to evaluate.”

Being very low on the curve is also not cause for automatic concern. If a child is under the 3rd percentile, the pediatrician may want to more closely monitor the baby for failure to thrive, says Dr. Amin. “However, I like to look at this as a big picture,” she says. “We do see some genetically small children, so if they’re on the lower percentile but meeting milestones, sleeping and are overall content with no other physical complaints, we can monitor.”

While pediatricians monitor a baby’s growth at regular appointments, it’s important to know when you should seek help in between visits. If you’re concerned about your baby’s weight gain and there are other symptoms, like reflux, blood in the stool or poor sleep—which Dr. Amin defines as a baby being unable to sleep three-hour stretches by 1 month old—call the pediatrician.

Monitoring your baby’s weight and length with the WHO growth charts is a way of making sure they are growing properly in the first year of their life. Knowing average baby weight and length can be helpful, but remember that the exact number doesn’t matter as much as linear growth over time.