A full-term newborn is typically 19 to 20 inches long (49 to 50 cm), though anything from 18.5 to 20.9 inches (47 to 53 cm) falls within the normal range. By their first birthday, most babies have grown to roughly 50% longer than they were at birth. Here’s what to expect at each stage and what influences your baby’s length.
Length at Birth
Most full-term babies measure between 19 and 20 inches from head to heel. That said, a baby born at 18.5 inches or 20.9 inches is still considered perfectly normal. Boys tend to measure slightly longer than girls at birth, but the overlap is large enough that the difference rarely matters in practice.
You’ll notice doctors and nurses refer to a baby’s “length” rather than “height.” That’s not just a word choice. Until age 2, babies are measured lying flat on their backs (called recumbent length), because they can’t stand reliably. Once a child can stand easily, the measurement switches to standing height. The two numbers aren’t identical: lying down typically gives a slightly longer reading than standing up, so the distinction matters when tracking growth over time.
How Fast Babies Grow in the First Year
Growth in the first year is faster than at any other point in life. From birth to about 6 months, babies grow roughly 1 inch (2.5 cm) per month. From 7 to 12 months, that pace slows to about half an inch (1.3 cm) per month. Add it all up and most babies gain around 9 to 10 inches in their first year, putting the average 12-month-old somewhere around 28 to 30 inches long.
That growth doesn’t happen at a steady, predictable clip. Babies go through distinct growth spurts, typically around 2 to 3 weeks, 6 weeks, 3 months, 6 months, and 9 months. During a spurt, your baby may seem hungrier than usual, fussier, or want to nurse or bottle-feed more frequently. These bursts usually last only a few days, with calmer stretches in between.
What Influences a Baby’s Length
Genetics is the single biggest factor. Taller parents generally have longer babies, and this influence only grows stronger as a child ages. But genes aren’t the whole story during pregnancy and infancy. Maternal nutrition, overall health during pregnancy, and whether the baby arrived early or on time all play a role. Babies born to mothers who smoked during pregnancy or who had poorly managed gestational diabetes, for example, can fall outside the typical range.
After birth, feeding matters. Breastfed and formula-fed babies grow at slightly different rates in the first year, which is one reason the growth charts used for infants are designed around breastfed growth patterns (more on that below). Adequate calorie and nutrient intake keeps a baby tracking along their growth curve, while prolonged illness or feeding difficulties can temporarily slow things down.
How Growth Is Tracked
Pediatricians plot your baby’s length on a standardized growth chart at each well-child visit. For children from birth to age 2, the CDC recommends using the World Health Organization (WHO) growth standards. These charts are based on healthy breastfed infants from multiple countries and represent how babies should grow under optimal conditions. At age 2, doctors transition to the CDC’s own growth charts, which cover children and adolescents up to age 20.
What matters most isn’t a single measurement but the pattern over time. A baby who consistently tracks along the 25th percentile is growing normally, even though they’re shorter than 75% of peers. A sudden jump or drop across multiple percentile lines is what signals a potential issue worth investigating.
Measuring Your Baby at Home
Getting an accurate length at home is trickier than it sounds. The gold standard involves laying the baby flat on a firm surface with their head touching a fixed headboard and a movable footpiece pressed gently against their heels. Both legs need to be fully extended with toes pointing up. Clinical guidelines actually recommend two people for the job: one to hold the baby’s head in position (eyes looking straight up, chin neither tucked nor tilted back) and another to straighten the legs and read the measurement.
If you’re measuring at home with a tape measure, you can approximate this by laying your baby on a flat surface, marking the top of the head and the bottom of the heel with a pencil, then measuring between the marks. Just know that home measurements are less precise, so don’t worry if your number doesn’t match the pediatrician’s exactly.
Premature Babies and Catch-Up Growth
Babies born early are typically shorter than full-term newborns, sometimes significantly so. Doctors track their growth using a “corrected age,” which adjusts for how early they arrived. A baby born two months premature, for instance, is compared to babies two months younger on the growth chart.
Most preemies experience catch-up growth that narrows the gap with their full-term peers by 12 to 18 months of corrected age. For some children, this catch-up period extends longer, continuing gradually for up to 5 to 7 years. The timeline depends on how early the baby was born, birth weight, nutrition, and whether there were complications during the newborn period.
Can You Predict Adult Height?
Birth length is a poor predictor of adult height. Too many variables, from nutrition to puberty timing, still lie ahead. By age 2, though, the picture sharpens considerably. A common rule of thumb is to double a child’s height at age 2: boys typically end up slightly taller than that number and girls slightly shorter. This works because most children have settled onto the growth chart percentile they’ll follow through childhood by the time they turn 2. It’s a rough estimate, not a guarantee, but it’s surprisingly reasonable for a back-of-the-napkin calculation.