The average newborn is 19.5 inches long and weighs 7.25 pounds. Boys have a head circumference of about 13.5 inches and girls measure in at 13.3 inches, according to the National Center for Health Statistics.
Birth to 4 Days Old
A baby drops 5 to 10 percent of his total body weight in his first few days of life because of the fluid he loses through urine and stool, says Parents advisor Ari Brown, M.D., author of Baby 411.
5 Days to 3 Months
Babies gain about an ounce a day on average during this period, or half a pound per week, and they should be back to their birthweight by their second-week visit. Expect a growth surge around 3 weeks and then another one at 6 weeks.
3 Months to 6 Months
A baby should gain about half a pound every two weeks. By 6 months, she should have doubled her birthweight.
7 Months to 12 Months
A child is still gaining about a pound a month. If you're nursing, your baby may not gain quite this much, or he may dip slightly from one percentile to another on the growth chart. "At this point, babies may also burn more calories because they're starting to crawl or cruise," says Tanya Altmann, M.D., a Los Angeles pediatrician and author of Mommy Calls. Even so, by the time he reaches his first birthday, expect him to have grown 10 inches in length and tripled his birthweight and his head to have grown by about 4 inches.
Growth for Toddlers, Preschoolers, and Big Kids
Toddlers will grow at a slower pace this year but will gain about a half a pound a month and will grow a total of about 4 or 5 inches in height.
A kid will sprout about 3 more inches by the end of her third year and will have quadrupled her birthweight by gaining about 4 more pounds. By now, your pediatrician will be able to make a fairly accurate prediction about her adult height.
Ages 3 and 4
A preschooler will grow about 3 inches and gain 4 pounds each year. You may also find that your child starts to shed the baby fat from his face and looks lankier, since kids' limbs grow more by the time they are preschoolers, says Daniel Rauch, M.D., associate professor of pediatrics at Mount Sinai School of Medicine, in New York City.
Kids will grow about 2 inches and gain 4 pounds each year until puberty (usually between 8 and 13 for girls and 10 and 14 for boys). Girls often reach their full height about two years after their first period. Boys usually hit their adult height around age 17.
How Tall Will Your Baby Be?
Most pediatricians do a rough estimate based on the following formulas:
For Boys Add 5 inches to Mom's height and average that number with Dad's height.
For Girls Subtract 5 inches from Dad's height, and average that number with Mom's height.
Originally published in the March 2011 issue of Parents magazine.