The average full-term newborn measures about 50 centimeters, or roughly 19.7 inches, at birth. Most babies fall within a range of 18 to 22 inches (46 to 56 cm), with slight differences between boys and girls. This measurement is one of the first things recorded after delivery and serves as a baseline for tracking your baby’s growth.
What the Numbers Look Like
International growth standards place the mean length for a boy born at 40 weeks at 49.9 cm (about 19.7 inches). Girls average slightly shorter, typically around 49.1 cm (19.3 inches). These figures come from the INTERGROWTH-21st project, which studied healthy pregnancies across six countries to define how babies grow under optimal conditions.
Babies born a week or two early tend to be a bit shorter, while those born past their due date may measure slightly longer. Genetics play a role too. Taller parents generally have longer babies, though the correlation is modest at birth and becomes more noticeable in the toddler years.
How Birth Length Is Measured
Newborn length is measured lying down, a technique called recumbent length. It requires two people: one holds the baby’s head flat against a fixed headboard while the other straightens the legs and slides a footboard snugly against the heels. The baby’s shoulders, back, and buttocks should all rest flat along the center of the measuring board, with eyes looking straight up. The imaginary line from the ear hole to the lower eye socket should be perpendicular to the board.
This sounds fussy, and it is. Newborns naturally curl their legs, squirm, and resist being stretched out. That’s why hospital measurements can vary by a quarter inch or more between attempts. Two readings that agree within an eighth of an inch are considered acceptable. If the number on your discharge paperwork seems different from what you heard in the delivery room, small discrepancies are normal and not a cause for concern.
What the Growth Charts Track
In the United States, the CDC recommends using the World Health Organization (WHO) growth charts for all children from birth through age 2. These charts are based on international standards describing how healthy, breastfed children grow in supportive environments. After age 2, clinicians switch to the CDC’s own reference charts, which reflect growth patterns of American children measured primarily during the 1970s through 1990s.
Your baby’s length will be plotted as a percentile. A baby at the 50th percentile is exactly average. One at the 25th percentile is shorter than 75% of babies the same age and sex, but that doesn’t necessarily signal a problem. What matters most is the trend over time. A baby who consistently tracks along the 20th percentile is growing normally. A baby who drops from the 60th to the 10th over several visits warrants a closer look.
When Birth Length Falls Outside the Typical Range
Babies whose weight, length, or both fall below the 10th percentile for their gestational age are classified as small for gestational age (SGA). The pattern of smallness can offer clues about timing and cause. When a baby is proportionally small (head, length, and weight all equally affected), the growth restriction often began early in pregnancy, sometimes in the first trimester, and affects overall cell production. When weight is low but head size and length are relatively preserved, the restriction typically started later, in the late second or third trimester, and is more commonly related to placental function or maternal health conditions.
On the other end, babies who measure above the 90th percentile are considered large for gestational age. This can occur with gestational diabetes, genetic factors, or simply because of family size patterns. In most cases, a baby on either end of the spectrum catches up or settles into a more typical growth curve within the first year.
How Fast Newborns Grow
In the first month alone, babies typically grow 1.5 to 2 inches (3.8 to 5 cm) in length. That pace is faster than at any other point in life outside the womb. Growth then gradually slows: most infants gain about an inch per month from months two through six, and roughly half an inch per month from six months to their first birthday. By 12 months, the average baby is about 29 to 30 inches long, roughly 50% longer than at birth.
These are averages. Healthy babies sometimes grow in spurts, adding length quickly over a few days and then plateauing. If your baby seems fussy, hungrier than usual, and sleeping more, a growth spurt is a likely explanation. Pediatricians track length at each well-child visit during the first year precisely because the pace of growth in this period is so rapid and so variable.