The average length of a full-term newborn baby is 19–20 inches (in), or 49–50 centimeters (cm). However, a length of around 18.5–20.9 in, or 47–53 cm, is also normal.
Male babies are slightly longer than female babies. Doctors measure a baby’s length from the top of their head to the heel of their foot.
In this article, we look at the average baby lengths, month-by-month, for the first year of life. We also discuss what it means when a baby is shorter or longer than average, and when to see a doctor.
Average baby sizes through the first year
The World Health Organization (WHO) publish standard infant growth charts based on the standard growth of children in six countries, including the United States, in optimal growth environments. This includes breastfeeding.
These numbers are just averages. Children can be healthy at a wide range of heights. No matter how long a baby is at birth, they are likely to grow at similar rates to other babies.
This means that if a baby is born longer than average, they are likely to stay this way during their first year or two of growth.
Growth in length during the first year is almost always based on length at birth, unless a baby has significant problems with poor weight gain that makes it difficult to thrive. This means a baby can have a lot of trouble with weight gain in the first year before it affects growth in length.
Unlike weight, which doctors objectively measured by a scale, the measured length of a baby can vary based on who is doing the measuring and how much the baby is moving around at the time.
Sometimes, if it seems as though there is an unexpected change in a baby’s length from one visit to the next, it can be due to differences in the measuring.
Length alone does not reveal whether a baby is healthy. Weight is also an important consideration, especially since many newborns lose some weight after birth. Doctors will also look at factors including gestational age and how much and how well a baby is eating.
Most healthy babies follow a similar growth pattern during the first year of life. After that, growth rates vary among infants, and a baby’s length is not usually a good predictor of their height as an adult.
What does it mean if a baby is small or large?
Children can be healthy at a wide range of heights.
Babies who are much smaller or larger than average in weight and length are more likely to experience health complications.
However, there is a wide variation of healthy birth weights, so caregivers may not need to worry. A doctor will assess how closely they need to monitor a baby’s growth over time.
Growth rates for length are fairly predictable among babies in the first year of life. Doctors are more interested in a baby’s growth pattern than their length.
A baby whose growth slows down such that they fall to a much lower length group, or whose length is persistently at a lower level, may have a health issue.
According to Centers for Disease Control and Prevention (CDC), a child who falls below the fifth percentile may have an abnormal growth pattern.
Numerous factors affect a child’s height. Genetics play a major role, and children are likely to be a similar height to their parents.
However, this may not be apparent right away, as a baby who will be a tall adult may have a shorter length at birth and in the first year or two of life.
Other factors affecting a baby’s length and overall size later on include:
- Nutrition. The consumption of healthy food supports healthy growth.
- Hormones. Some children with hormonal imbalances grow slowly or more quickly than their peers.
- Health. Some children with certain genetic conditions, such as Down syndrome, may be smaller than others. Certain health conditions, such as juvenile arthritis, can also affect growth.
- Medication. Some medications, such as steroid drugs including prednisone, may stunt growth.
People often do not see the effect of these issues on height in the first year of life.
When to see a doctor
During the first year of life, children should see their pediatrician at least seven times to monitor growth and overall health.
Doctors’ recommendations may vary slightly. In general, a pediatrician will want to see a baby:
- 3–5 days after birth
- 7–14 days after birth, or sometimes 1 month
- at 2 months
- at 4 months
- at 6 months
- at 9 months
- at 12 months
A doctor may recommend more frequent visits for a baby who loses a lot of weight after birth, or who has an unusual growth pattern.
How much to feed newborns
Breastfed newborns can eat every 1–3 hours.
The amount of food a newborn eats affects their weight much more than their length in the early stages of life. Poor weight gain needs to be present for a long time in infants before it affects their length.
Poor growth in length by itself in the first year is very uncommon and would more likely be due to a genetic syndrome or other uncommon condition.
In the early weeks of life, it can be difficult for caregivers to know how much to feed a newborn. If the baby loses weight after birth, parents may feel pressure to help the baby regain the weight as quickly as possible, especially if the baby was born prematurely or has other health risk factors.
Most breastfed newborns eat every 1–3 hours, but formula-fed babies may eat less frequently than this.
After the first few days, people typically feed formula-fed babies with 1–2 ounces (oz) of milk per feeding, which may increase to 2–4 oz by the end of the first month.
It can be hard to tell how much milk an exclusively breastfed baby consumes. People can feed the baby on demand by following the baby’s feeding cues.
Some signs that indicate a baby is hungry include:
- opening their mouth and turning their head to the side
- smacking their lips
- licking their lips
- trying to suck on things
- trying to put their hands or fingers in their mouths
Newborns typically need to eat several times each night to sustain healthy growth.
If a baby does not gain weight by consuming breast milk, a pediatrician and lactation consultant may be able to help. Sometimes, the problem is that the mother does not produce enough milk.
The problem may also be that the baby has trouble effectively sucking. With the right help, however, most babies are able to breastfeed.
Like adults, babies are unique.
There is no right length. As long as a baby is growing normally and does not suddenly fall well below their previous growth percentile, they are usually fine.
A pediatrician can help caregivers answer questions about length, growth, nutrition, and much more.
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