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Information for Parents

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What do regular measurements tell us?

Weighing and measuring helps us to check that your child is growing and developing as expected.

Why do we use growth charts?

The lines on a growth chart are called "centile lines". They are based on measurements from many infants and children. They show the optimal range of weights, lengths and head circumferences for healthy children, and how one child compares with others of the same age and sex.

For example, if your child’s weight is on the 25th centile, it means that if you lined up 100 children of the same age and sex in order of weight, your child would probably be number 25; 75 children would be heavier than your child, and 24 would be lighter. Weights, lengths and head circumferences that are anywhere within the centile lines on the chart are considered normal.

Every child is different (they come in all shapes and sizes!), so no two filled-in charts will look the same. Even twins may have different growth patterns.

If a child’s growth pattern looks unusual, your health visitor or doctor may want to have a closer look to see why. This may involve taking more measurements or performing investigations. Most children who have such investigations are found to be perfectly normal, however, it is important to check unusual patterns just to make sure.

The UK-WHO growth charts

The UK-WHO growth charts are based on data from 2 different sources, depending on a child's age:

Birth - 4 years uses WHO data

The World Health Organisation (WHO) collected measurements from healthy term babies (born after 37 weeks of pregnancy or more) in 6 different countries. These were healthy, breast-fed babies whose mothers did not smoke, had good access to healthcare and nutrition. Their measurements were recorded over time. The centile curves drawn using these measurements show how healthy babies are expected to grow - regardless of ethnic origin, or breast / formula-fed. For preterm babies (born before 37 weeks pregnancy), measurements are plotted on growth charts based on the birthweights of British infants who were born prematurely.

4 years - 20 years uses UK1990 data

Many measurements of British children, aged between 4 and 20 years, were collected in the 1980-90s. These centiles show similar healthy growth trends for these ages.

Weighing and measuring

Up to 2 years of age, children should be weighed without any clothes or nappy on, as this can make a big difference to the weight. Be aware that different scales sometimes give different readings, particularly if they are not electronic. If you notice this, try to take your baby/child to the same place for weighing each time.

Up to the age of 2 years, your child is measured for length (i.e. lying down) rather than height. Special equipment is needed to measure length accurately, which will be recommended by a health care professional if needed. Your child should not be wearing a nappy when their length is measured.

After 2 years of age, your child’s standing height should be measured. Your child’s shoes should be removed during the measurement. It is important to measure height accurately using a rigid rule with T piece or stadiometer.

From age 4 years, your child’s Body Mass Index (BMI) can be calculated from their weight and height:


BMI is a crude measure of fatness or thinness, and high levels suggest the child may be carrying too much fat. The cut-offs for a high BMI in children are different from those used in adults and depend on age. Some medical conditions or treatments your child receives may mean the BMI centile is not the best way to measure your child. A low BMI can be due to a relatively low amount of lean (muscle) tissue as well as fat. Your GP or other health professional caring for your child will be able to discuss your child’s BMI with you.

How often to weigh

It is normal for a baby to lose some weight in the first few days after birth. Your baby should be weighed in the first week as part of the assessment of feeding. Most babies get back to their birth weight by 2 weeks of age. This is a sign feeding is going well, and your baby is healthy.

After 2 weeks, your baby will usually be weighed only when seen routinely, unless there is concern. Weighing your baby too often can cause unnecessary concern; the list below shows how often, as a maximum, babies should be weighed to monitor their growth. However, most children will not need to be weighed as often as this.

Many parents like to have their babies weighed more often. However, it is not always helpful and can cause unnecessary worry. For example, if one week your baby was weighed just after a big feed, but the next week they were weighed after a long nap and before a feed, it could look as if they had not gained weight. Longer gaps between weights are more likely to show the true weight change.

The recommended time between weighing increases as babies age because they grow more slowly.

Your health visitor or doctor may recommend more frequent weighing for children if there are concerns about their growth or health, or if they have certain medical conditions. If there are serious concerns about slow weight gain or even weight loss, a child could be weighed as often as:

  • daily if less than 1 month old
  • weekly between 1–6 months old
  • fortnightly between 6–12 months
  • monthly from 1 year of age

Remember that if you want advice you can always phone your health visitor or visit the clinic, without having your child weighed.

Beyond the age of two years, children need only be weighed if there are worries about their health, growth or poor weight gain. Once they go to school, in England, they will be measured with their classmates for the National Child Measurement Programme in their reception class and their last year in primary school.