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Normal baby size at birth

The arrival of a new baby can also raise many questions from first-time parents, who are often worried about the health of their new bundle of joy. Among the questions will be, "Is the baby's size normal?"

When a baby is born his or her weight and length will be measured, as well as their head circumference. The health of the mother, including her weight, diet, medical conditions such as heart problems, and whether or not she smoked cigarettes or drank alcohol, and the family history of both parents will help determine the baby's size. If the parents are tall or small, the baby is likely to be the same. The baby may arrive early, meaning a smaller baby, or late and therefore larger. Even the baby's gender can make a difference: girls tend to be smaller than boys.

Often a baby is larger or smaller than average but is still healthy. Although a baby is small or big at birth, it does not necessarily reflect his or her adult size. Small babies who are born early can become tall adults, for example.

What is considered the normal weight for a newborn?

The normal weight of a baby who reaches full term between 37 and 40 weeks is 2.7–4.1kg (6 – 9 lbs), with an average weight of 3.5kg (7.7 lbs).

A baby who weighs less than 2.5kg (5.5 lbs) is considered to have a low birth weight. About half of all twins and 90% of all triplets are born prematurely, before 37 weeks, and have a low birth weight of under 2.5kg.

A baby who weighs more than 4kg (8.8lbs) at birth may be referred to as macrosomia, which means the baby is larger than normal. These babies are often born to mothers who developed gestational diabetes while they were pregnant. You may also have a large baby if:

  • You were a big baby yourself
  • You were overweight before becoming pregnant
  • You gain lots of weight during the pregnancy
  • The baby is born more than two weeks past the estimated due date


What is the normal length of a newborn?

The normal length of a baby who reaches full term is 50–53cm long, with an average length of 51cm. Babies of tall parents are likely to be longer, while those of short parents are often shorter.

Should I be concerned if my newborn is losing weight?

Newborns are born with extra fluid, so their weight will drop by 7–10% in the several days after birth, but their birth weight should be regained by about 2 weeks.

The NHS will supply parents with growth charts in a 'red book' to provide a personal health record of the child as he or she grows. Plotting measurements along curved lines, known as centile lines, will give an indication of how the child's growth is progressing. The centile lines are based on data provided by the World Health Organisation (WHO) and represent the pattern of growth that healthy children should follow. The child's measurements should roughly follow the curve of the percentile line plotted at birth.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on February 10, 2016

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