Average Baby Weight and Length in the First Year

Like many 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 doctor will look at your child’s height, weight, and age to see if your child is growing as expected.

Factors affecting a baby's height/length
Verywell / Emily Roberts

Birth Weight

The World Health Organization has established standards for infant and child growth. The average weight of a newborn is around 7 to 7 1/2 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. They include:

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

Baby Weight Gain in the First Year

Again, every baby differs, but here's what you can generally expect in the first 12 months of life.

First two weeks: During the first few days of life, it's normal for both breastfed and bottle-fed newborns to lose weight. A bottle-fed baby may lose up to 5 percent of his body weight, and an exclusively breastfed newborn can lose up to 10 percent. But, within two weeks, most newborns regain all the weight they have lost and return to their birth weight.

By one month: Most infants will gain about a pound over their birth weight by month one. At this age, infants are not as sleepy, they begin developing a regular feeding pattern, and they have a stronger suck during feedings.

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

By one year: Between six months and one year, weight gain slows down a little. Most babies double their birth weight by five to six months of age and triple it by the time they are a year old. 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).

Weight Chart

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.

Average Baby Weight During the First Year
  Boys Girls
Age 50th Percentile 50th Percentile
1 Month 9 lbs 14 oz (4.5 kg) 9 lbs 4 oz (4.2 kg)
2 Months 12 lbs 5 oz (5.6 kg) 11 lbs 4 oz (5.1 kg)
3 Months 14 lbs (6.4 kg) 12 lbs 14 oz (5.8 kg)
4 Months 15 lbs 7 oz (7.0 kg) 14 lbs 2 oz (6.4 kg)
5 Months 16 lbs 9 oz (7.5 kg) 15 lbs 3 oz (6.9 kg)
6 Months 17 lbs 8 oz (7.9 kg) 16 lbs 2 oz (7.3 kg)
7 Months 18 lbs 5 oz (8.3 kg) 16 lbs 14 oz (7.6 kg)
8 Months 19 lbs (8.6 kg) 17 lbs 7 oz (7.9 kg)
9 Months 19 lbs 10 oz (8.9 kg) 18 lbs 2 oz (8.2 kg)
10 Months 20 lbs 3 oz (9.2 kg) 18 lbs 11 oz (8.5 kg)
11 Months 20 lbs 12 oz (9.4 kg) 19 lbs 4 oz (8.7 kg)
12 Months 21 lbs 3 oz (9.6 kg) 19 lbs 10 oz (8.9 kg)

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

How Does Breastfeeding Affect Weight?

While it is normal for a newborn to lose weight during the first few days of life, after that period, weight loss or poor weight gain in a child is a sign of a problem. For breastfed babies, it could mean that the baby is not getting enough breast milk.

When it comes to weight gain, breastfed babies are less likely than formula-fed infants to gain too much weight too quickly. Breastfeeding may even help to prevent excessive weight gain and obesity. However, breastfed babies can gain too much if a mother has an overabundant supply of breast milk, the child spends too much time nursing, or solid foods are started early.

Baby Length (Height) in the First Year

In general, during the first six months, a baby grows about one inch per month. Between six months and one year, that slows down a bit to about a 1/2 inch 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).

The factors that determine height are:

  • Genetics: The height of a child's mother, father, and other family members have the most significant impact on how tall the child will be.
  • Gender: Boys tend to be taller than girls.
  • Nutrition: Good nutrition for both mom during pregnancy and the baby after birth can ensure that the baby's body is getting 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.

Baby Length by Month

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

Average Baby Length Chart
  Boys Girls
Age 50th Percentile 50th Percentile
1 Month 21 1/2 in (54.7 cm) 21 in (53. 7 cm)
2 Months 23 in (58.4 cm) 22 1/2 in (57.1 cm)
3 Months 24 1/4 in (61.4 cm) 23 1/2 in (59.8 cm)
4 Months 25 1/4 in (63.9 cm) 24 1/2 in (62.1 cm)
5 Months 26 in (65.9 cm) 25 1/4 in (64.0 cm)
6 Months 26 1/2 in (67.6 cm) 25 3/4 in (65.7 cm)
7 Months 27 1/4 in (69.2 cm) 26 1/2 in (67.3 cm)
8 Months 27 3/4 in (70.6 cm) 27 in (68.7 cm)
9 Months 28 1/4 in (72.0 cm) 27 1/2 in (70.1 cm)
10 Months 28 3/4 in (73.3 cm) 28 in (71.5 cm)
11 Months 29 1/4 in (74.5 cm) 28 1/2 in (72.8 cm)
12 Months 29 3/4 in (75.7 cm) 29 in (74.0 cm)
*Inches are rounded to the nearest 1/4 inch.

Infant Growth Spurts

Infants don't grow at a consistent rate. They have times when they grow slowly and times when they experience more rapid growth. A big surge of growth that occurs in a short period of time is known as a growth spurt.

Growth spurts can happen at any time, and they do not necessarily follow a pattern. Some of the ages that your child may experience a growth spurt are at ten days, three weeks, six weeks, three months, and six months.

During and after a growth spurt, your baby will need more milk. You may need to feed your baby as much as every hour or two, a phenomenon often referred to as cluster feeding.

This tends to happen more often with breastfed babies. Since breast milk is made based on supply and demand, your baby will breastfeed much more often around the time of a growth spurt, signaling your body to make more milk. Luckily, these frequent feedings only last about a day or two as your milk supply adjusts to your growing baby's needs. After that, your child should settle back down into a more regular feeding routine.

Growth Chart Considerations

Growth charts and percentiles are just tools that help 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 certainly doesn't mean that he or she is not growing at a healthy rate. Healthy infants can be in the 5th percentile as well as the 95th percentile.

While it may be tempting to compare your child’s growth and development to other children, it is important to remember that babies come in all shapes and sizes.

Growth depends on many factors, including genetics, diet, and activity level. Every child grows at his or her own pace, and doctors look to make sure kids are on track for what is expected for them given their history. It's difficult to compare one child to another, even if they are brothers and sisters.

Not All Growth Charts Are Equal

Just as all children are different, it is 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. Since mothers are breastfeeding more and more 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 are breastfeeding or taking formula) during the first two years. The American Academy of Pediatrics (APP) agrees with the CDC recommendation.

A Word From Verywell

When you compare your child to other babies, you may worry if you notice that he is smaller or heavier than his peers. Luckily, there is an easy way to ease your fears and find out for sure if your child is growing as expected. You just have to follow the regular schedule for well-child visits that your healthcare provider gives you.

The doctor will weigh and measure your baby each time you see him. And, he will keep track of your child's growth and overall health over time. This will allow him to notice any diversions from your child's anticipated growth, based on history, and address any possible concerns quickly, if applicable.

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Article Sources

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  2. Carling SJ, Demment MM, Kjolhede CL, Olson CM. Breastfeeding duration and weight gain trajectory in infancy. Pediatrics. 2015;135(1):111-9. doi:10.1542/peds.2014-1392

  3. Growth. La Leche League International. https://www.llli.org/breastfeeding-info/growth/.

  4. Growth Charts - Homepage. Centers for Disease Control and Prevention. https://www.cdc.gov/growthcharts/index.htm. Published September 9, 2010.