What Is the Average Growth of an Infant From Zero to Eleven Months Old?

Although infants grow at different rates, there are some standards for measurement, including length, weight and developmental skills that can be used to gauge the health of an 11-month-old. On average, babies grow from about 7 lbs. at birth to about 21 lbs. by 11 months. Growth averages are specific to an infant's sex and age and are tracked by charts from the Centers for Disease Control and Prevention, or CDC.

Four mother's and their babies. (Image: Digital Vision./Digital Vision/Getty Images)

Weight

According to healthy weight ranges compiled by the CDC, infant boys at 11 months who weigh around 21 lbs. on track with about 50 percent of their peers. For females, this number is approximately 19 lbs. Boys average 7 lbs. at birth, so the growth rate is about 1.2 lbs. per month. Female infants average a growth rate of about 1 lb. per month.

Length

Eleven-month-old boys who measure approximately 29 inches in length are equal to 50 percent of their peers. According to the CDC charts, newborn boys average 20 inches in length, so the average growth is approximately .82 inches per month. Newborn girls average 19.5 inches at birth and 28 inches by 11 months, so their average growth rate in length is approximately .86 inches per month.

Skill Development

Infant growth is also measured in terms of developmental stages. From zero to 11 months, infants have undergone many changes in motor skills, including holding their heads up, crawling and teething. At 11 months, infants are generally standing on their own and attempting to walk. New motor skills may include feeding themselves and waving at familiar people. Skill development can be highly subjective for an infant, so it's important to incorporate this measurement of growth with other indicators like weight and length.

Considerations

These estimates of average growth from birth to eleven months are based on the mean data presented in the CDC growth charts and should only be used as a rough gauge for healthy growth. Infants at the higher end of the growth spectrum weigh more and measure longer in length, and those on the lower spectrum measure less than the average in both weight and height. If you are concerned with your child's growth, consult a physician for a thorough health assessment.