Measure your baby’s length by measuring from the top of the head to the bottom of the heels. This is similar to calculating the height. The only difference is that height is measured when a baby is standing. For length, babies lie prone on their backs.
When babies are measured, a pediatrician will measure the length, weight and the circumference of the head. The average newborn length of a full-term baby at birth is around 19 to 20 inches or about 50 cm with a head circumference of 13 ½ inches. This range tends to vary from 18 inches to 22 inches or 45.7 to 60 cm. Babies grow up to an inch each month up to six months of age. From 6 months onwards, your baby will grow up to a centimeter per month which your doctor can measure by weighing your infant at every checkup to determine if they are following the growth size chart.
There are some babies who experience growth spurts during the first 10 to 14 days, 5 to 6 weeks and at 3 or 4 months. During growth spurts, babies tend to be fussier than normal and feed more. These growth spurts can last up to a week [1].
A baby’s head and brain undergo 80% of their growing during the first 2 years of life. Doctors track the brain and head’s growth as the skull fuses by measuring the head circumference.
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Factors To Consider When Measuring The Average Newborn Length
Knowing the average newborn length can help you determine whether your newborn baby is in a larger or smaller size percentile. Babies come in all sizes and shapes, and baby diapers go by weight.
Babies who are a larger size at birth meaning bigger and longer than average can be so for the following reasons:
- Parents are larger than average size adults.
- Baby boys tend to be larger than baby girls.
- A baby is born beyond full-term.
- The mother has gestational diabetes which is a type of diabetes that develops during pregnancy.
Adversely, newborn babies who are a smaller size at birth or born smaller than average can be so for the following reasons:
- Parents are smaller than average.
- Girls tend to be smaller than boys.
- Nutrition was poor during the pregnancy.
- Health conditions such as asthma or high blood pressure were present during pregnancy.
- The mother took drugs, drank alcohol or smoked during the pregnancy.
What To Expect In Early Checkups
First-time mothers and fathers may become worried if their baby’s weight decreases during the first few days after birth. There is no need to feel alarmed. This is entirely normal because infants are born with extra fluids that will be eliminated thus causing their weights to go down. Weight gain starts to occur after five days, so by day 10 babies have most likely regained the weight that they lost.
Your pediatrician will monitor your baby’s height and weight and head circumference based on a standard growth chart. This chart determines how fast your baby has grown compared to other babies of the same age. The following details what to expect during the early checkups of your baby.
Birth to 1-month-old
The average length of a newborn is 20 inches. Babies grow an additional 1 to ½ an inch in length and gain 2/3 an ounce of weight within the first month.
3 months
Babies at this point will be gaining up to 2 pounds and lengthening another 1½ inches from the second to the third month. Your baby may appear chubby. Babies may flip on their stomachs at this point which helps them develop their muscles.
6 months
Most babies have gained twice the amount of their birth weight at this point.
12 months
Babies who have reached the first year may have tripled their birth weight and will have grown 22.86 to 27.94 or 9 to 11-centimeter inches respectively.
24 months
At this point, your baby’s weight may have quadrupled with their length ranging from 14 to 16 inches compared to their length at birth.
Understanding The Physical Growth Of Average Newborn Length
During pregnancy, fetal growth is closely monitored by doctors to ensure proper development. Now that you have given birth, there are many physical changes to expect during the first month.
Average weight of a newborn
The average newborn weight for a full-term baby is pegged at 7 lb. 11 oz. with a normal weight ranging from 5 lb. 8 oz to 8 lb. 13 oz. Your baby’s weight will vary depending on their sex, genetics and care while in the womb. Typically, babies lose weight during the first five days since they are eliminating the excess fluids from their body, but they quickly gain back their birth weight afterward whether they are formula or breastfed babies.
Average length of a newborn at birth
The average length of a full-term baby at birth is 20 inches although the normal range is 18 inches [6].
Average head circumference of a newborn
The average head circumference of a newborn is around 13 to 14 inches, which is 1-inch greater than the measurements of their chest and abdomen. Take note that the circumference can change depending on whether it was a normal delivery or a breech birth where the feet appear before the head.
A pediatrician will monitor your baby’s growth through the weight, length and circumference of the baby’s head every check-up. This way, your pediatrician will determine which percentile your little one falls under during the first few months or years.
Keep An Eye On Your Baby’s Weight And Height
Aside from knowing what the average newborn length is, monitor your little one’s weight to determine if your baby is growing during their first few months. As mentioned before, newborn babies shed some birth weight during the first few days which they can gain back afterward. Around 2 weeks, babies are weighed and measured to determine if they regained their birth weights.
For babies who lost weight, monitor breastfeeding to ensure that your little one is getting enough milk, or take note of the amounts and feeding times for formula-fed babies. A special care nursery can help feed your little one until the weight returns.
After the standard two weeks, infants are weighed once a month until they reach six months. The succeeding months, measurements are limited to once every 2 months to see if there are any changes to weight and length. By the first year and beyond, infants are weighed once every three months. Your baby should show signs of lengthening comparable to the average length of a newborn.
A baby’s weight fluctuates, and growth spurts will occur during the first six to nine months which means that there will be plenty of soiled and wet diapers to change. A baby’s stomach is growing to accommodate more food. Check the average diapers per month for a good indication that your baby is steadily growing. If your baby does not produce around the average diapers per month based on age, it is likely that your baby requires more food [2].
Factors That Affect The Average Newborn Length
Normally, babies grow up to an inch per month from birth to six months. As they go beyond the sixth month to 12 months, their growth rate slows to half an inch per month. A baby boy’s average length at six months is around 26.5 inches or 67.6 centimeters, while a baby girl will be around 25.75 inches or 65.7 centimeters. By the time baby boys reach their first year, their length will be at 29.75 inches while girls measure at 29 inches.
Sometimes, a child’s skeletal age must be determined. A skeletal age assessment (SAA) is a clinical procedure used to determine the skeletal age of children and teens [3]. An SAA assesses skeletal maturity, growth potential and growth disorders such as growth hormone deficiency and hypothyroidism. A single x-ray is taken of the left wrist, hand and fingers. This is compared with a standard atlas of the same bones from large numbers of other children of the same gender and age [4].
Bone development can be influenced by nutrition, hormonal secretions and genetics.
There are many factors that affect a baby’s size:
Gender
A study shows that baby boys are usually bigger than baby girls.
Genetics
How tall your little one will be when they grow up is impacted by genes from both of the parents’ sides. If the parents are taller than average, expect the baby to grow tall.
Sleep pattern
There are studies that point to infants growing in length after getting long periods of sleep and naps.
Nutrition
Nutrition affects a baby’s growth. Your baby’s nutrition begins in your womb, so pay attention to what you are eating while you are pregnant. Your baby needs to absorb important nutrients such as vitamins, minerals, and protein which are essential to overall growth. This will continue after birth as your baby will be drinking breast milk during the first few months.
Physical activity
Your little one’s activity can also affect their growth. The more a child is active, the better the muscle and bone development will be.
Overall health
Another factor that affects infants’ growth is their state of overall health during the first few months. If your baby is prone to illness, they may not be growing at a fast rate.
What You Need To Know About Infant Growth Spurts
Some babies born are longer and bigger compared to others of the same sex and age. Infants are individuals and do not always grow the same as the others. There are instances where a baby grows at a rapid rate then slows down all of a sudden. If you notice that your baby has grown quite a bit in a short amount of time, this is referred to as a growth spurt which can occur at any time. It is possible that your little one will experience this at ten days, three to six weeks or three and six months.
Babies require more feeding during growth spurts regardless of whether they are breastfed babies or formula-fed infants. Growth spurts are usually bigger in breastfed infants compared to those who are formula-fed. Regardless, growth should continue as your baby gets older day by day. Since your baby will be demanding more milk, your body will be producing more milk. Your baby’s need for more milk during a growth spurt will only last a day or two, and eventually, both parties will settle into a more normal feeding routine.
The average length of a newborn can be used as a guideline to determine whether your baby is small, normal or above average in length. With the charts provided by your pediatrician, you will be able to determine if your little one is developing at a typical pace [5].
Average Newborn Length Resources:
[1] Centers for Disease Control and Prevention; WHO Growth Standards Are Recommended for Use in the U.S. for Infants and Children 0 to 2 Years of Age.[2] National Health Service (NHS); Your pregnancy and baby guide, Your baby’s weight and height, November 02, 2017.
[3] US National Library of Medicine, National Institutes of Health; Hand X-ray in pediatric endocrinology: Skeletal age assessment and beyond, Vincenzo De Sanctis, Salvatore Di Maio, Ashraf T. Soliman, Giuseppe Raiola, Rania Elalaily, Giuseppe Millimaggi, Novmeber 2014.
[4] KidsHealth from Nemours; X-Ray Exam: Bone Age Study, Yamini Durani, MD, May 2014.
[5] US National Library of Medicine, National Institutes of Health; Boys Live Dangerously In The Womb, Johan G. Eriksson, Eero Kajantie, Clive Osmond, Kent Thornburg, David J.P. Barker, May 2010.
[6] University of Michigan, Michigan Medicine; Physical Growth in Newborns Susan C. Kim, MD, Kathleen Romito, March 27, 2018.
