Average Baby Weight and Length: Month-by-Month Charts

Your baby's exact weight is less important than their overall growth trend. Here's what to know for every age and stage.

Medically reviewed by Candice W. Jones, MD FAAP

Like many new parents, you might be wondering if your baby is growing normally. Healthy babies can be a range of sizes, but the course of development tends to be fairly predictable. At checkups, a pediatrician will check your child’s height, weight, and age to see if they're growing as expected. Most importantly, they will look at how your baby's growth is progressing over time. Here's what to expect.

Average Baby Weight at Birth

The World Health Organization has established standards for infant and child growth. The average weight of a newborn is around 7 to 7.5 pounds (3.2 to 3.4 kg).

Most full-term healthy newborns weigh anywhere from 5 pounds 11 ounces to 8 pounds 6 ounces (2.6 to 3.8 kg). Low birth weight is less than 5 pounds 8 ounces (2.5 kg) at full term, and larger than average is a birth weight over 8 pounds 13 ounces (4.0 kg).

Many things can affect a newborn's birth weight, including:

• How many weeks a pregnancy lasts: Babies born prematurely are typically smaller, and babies born past their due date may be larger.

• Smoking: Birthing parents who smoke tend to have smaller babies.

• Gestational diabetes: Diabetes during pregnancy can lead to a larger-than-average baby.

• Nutritional status: Poor nutrition during pregnancy can lead to a smaller baby, whereas excessive weight gain can lead to a larger baby.

• Family history: Some babies are born smaller or larger, and it may just run in the family.

• Gender: On average, newborn baby girls weigh less than boys.

• A multiple pregnancy: A single baby will likely have a greater birth weight than siblings born in a multiples pregnancy (twins, triplets, etc.).
  

Related: Age-by-Age Guide to Your Kid's Height and Weight Growth

Average Weight Gain in the First Year

Again, every baby differs, but here's how much weight you can generally expect your baby to gain in the first 12 months of life.

Average Baby Weight in the First Two Weeks

During the first few days of life, it's normal for both breastfed and formula-fed newborns to lose weight. A bottle-fed baby may lose up to 5% of their body weight, and an exclusively breastfed newborn can lose up to 10%.

However, within two weeks, most newborns regain all the weight they've lost and return to their birth weight.

Average Baby Weight at One Month

Most infants will gain about 1 or 2 pounds by their first month. At this age, infants are not as sleepy, they begin developing a regular feeding pattern, and they have a stronger suck during feedings.

Related: The Most Lifelike Bottles for Breastfed Babies

Average Baby Weight at Two Months

Generally, babies this age will continue to gain about 1.5 to 2 pounds each month. This usually puts them at about 2 to 4 pounds over birth weight at 2 months old. The average weight at two months old is about 11 pounds 4 ounces (5.1 kg) for girls and 12 pounds 5 ounces (5.6 kg) for boys.

Average Baby Weight at Six Months

On average, babies gain about 1.5 to 2 pounds each month for the first six months. The average weight at 6 months is about 16 pounds 2 ounces (7.3 kg) for girls and 17 pounds 8 ounces (7.9 kg) for boys.

Average Baby Weight at One Year

After they turn 6 months old, your baby's weight gain slows down a little. Most babies double their birth weight by 4 to 6 months of age, and they triple it before their first birthday. By one year, the average weight of a baby girl is approximately 19 pounds 10 ounces (8.9 kg), with boys weighing about 21 pounds 3 ounces (9.6 kg).

Average Baby Weight Chart by Month

This growth chart is for healthy, full-term infants. A doctor may use specialized growth charts for premature babies or those born with special health needs.

If you have concerns about your child's growth, you should contact your health care provider. Your child's doctor is the best source of information when it comes to your child's growth and development.

How Breastfeeding Impacts Baby Weight

While it's normal for a newborn to lose weight during the first few days of life, after that period, weight loss or poor weight gain could indicate a problem. For breastfed babies, it could mean they're not getting enough breast milk.

On the other hand, breastfed babies can gain too much weight if a nursing parent has an overabundant supply of breast milk, the baby consumes excessive amounts of breast milk, or solid foods are started too early.

Average Baby Length (Height)

In general, during the first six months, a baby grows about one inch per month. Between six months and one year, that growth slows down to about 0.5 inches per month.

The average length of a baby boy at six months is approximately 26 1/2 inches (67.6 cm) and a baby girl is about 25 3/4 inches (65.7 cm). At one year, boys are around 29 3/4 inches (75.7 cm) and girls average 29 inches (74 cm).

Some factors that determine height are:

• Genetics: The height of a child's mother, father, and other family members has the most significant impact on how tall the child will be.

• Gender: Boys tend to be taller than girls.

• Nutrition: Good nutrition for both the parent during pregnancy and the baby after birth can ensure that the baby's body gets the proper vitamins, minerals, and protein for healthy bones and optimal growth.

• Sleep pattern: Studies show that infants grow in length after naps and long periods of sleep.

• Physical activity: Body movement and physical activity help build strong muscles and bones.

• Overall health: Chronic illness and disease during childhood can affect growth and development.

Average Baby Length Chart by Month

This chart shows the average length (or height) of healthy, full-term babies from one month to one year.

*Inches are rounded to the nearest 1/4 inch.

Baby Growth Chart Considerations

Growth charts and percentiles are just tools that track the growth of children over time. The 50th percentile means average, not "normal." While some children fall on the average line, many children fall below or above it. So, if your baby is not in the 50th percentile, it doesn't mean that they're growing at a healthy rate. Healthy infants can be in the 5th percentile as well as the 95th percentile.

Growth depends on many factors, including genetics, diet, and activity level. Every child grows at their own pace. Doctors make sure kids are on track for what's expected of them given their history. What matters most is that your child has a healthy growth trend, rather than how their height and weight compare to other children.

Baby Growth Spurts

Growth spurts can happen at any time, and they don't necessarily follow a pattern. Some of the ages that your child may experience a growth spurt are 2-3 weeks, 6 weeks, 3 months, and 6 months. During and after a growth spurt, your baby will need more milk. You might need to feed them as often as every hour or two, a phenomenon often referred to as cluster feeding.

Not All Growth Charts Are Equal

Just as all children are different, it's important to realize that not all growth charts are the same. The Centers for Disease Control and Prevention (CDC) provides a set of growth charts that include older data and information from a combination of feeding methods. The CDC growth charts are a reference and show how children grew during a specific period in the United States.

The World Health Organization (WHO) growth charts contain more data from breastfed babies. Mothers are nursing more frequently, and the WHO charts are considered a standard on how children should grow.

The CDC recommends using the WHO growth charts for all babies (whether they're breastfeeding or taking formula) during the first two years. The American Academy of Pediatrics (AAP) agrees with the CDC recommendation.

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