Average Newborn Baby Weight and Length

Normal Growth Patterns From Birth Through Infancy

Aug 19, 2009

Babies grow rapidly after birth, and the average infant triples his birth weight by his first birthday and grows about one inch per month during the first year

Babies grow rapidly in the womb for nine months, but the growing does not end there. An infant will usually triple his or her birth weight by the first year and grow 1.5 times longer than his or her birth length.

This rapid growth slows after a baby's first birthday, but by his or her third birthday, he or she will weigh about one-fourth of his or her adult weight and be nearly half of his or her adult height.

Average North American Newborn Height and Weight

On average, a North American newborn baby will be 7.5 pounds and 20 inches long. While there are vast variations in newborn height and weight, 95 percent of full-term newborns are 18 to 22 inches long and weigh 5.5 to 10 pounds. Premature births and special circumstances are the exception to these averages.

From birth, infants grow about 1 inch per month for the first year. By their first birthday, infants usually are 1.5 times longer than their birth length, having reached about one-third of their adult height.

Although newborns usually lose 5 to 7 percent of their birth weight during their first few days of life as they adjust to sucking, swallowing and digesting, they begin rapidly gaining weight shortly thereafter. The average newborn gains 5 to 6 ounces per week during the first month, and continues growing quickly from there.

By four months, babies have normally doubled their birth weight; by their first birthday, they weigh almost three times as much as they did when they were born.

Slower Growth After First Birthday

Though babies grow rapidly during their first year of life, their growth slows significantly during their second year of life. By a toddler's second birthday, he or she will weight about 26 to 32 pounds and will be 32 to 35 inches tall.

This means that by a child's second birthday, he or she weighs about one-fourth of his or her adult weight and has reached about half of his or her adult height.

Averages are not Always Accurate

Remember that babies grow at different rates due to different circumstances and these numbers are only averages. Talk to a pediatrician about proper growth rates for a baby or infant who may not be growing at an average rate.

Galloway, J.C. & Thelen, E. "Feet first: Object exploration in young infants." Infant Behavior and Development, 107-113.

The copyright of the article Average Newborn Baby Weight and Length in Infant Toddler Development is owned by Megan B. Wyatt. Permission to republish Average Newborn Baby Weight and Length in print or online must be granted by the author in writing.