Average Weight and Height for Children by Age in the UK

As a paediatric nutritionist with over 15 years of experience working with families across the NHS and private practice, one of the most common questions I hear from parents is: “Is my child the right weight and height for their age?” It is a perfectly natural concern, and understanding what is typical for UK children can offer reassurance or, when needed, prompt a helpful conversation with your GP or health visitor.

In this guide, I walk you through the average weight and height figures for children at every key age, explain how UK growth charts work, and help you understand what these numbers actually mean for your child’s health. I want to stress from the outset that every child grows at their own pace, and these averages are reference points rather than rigid targets.

Understanding UK Growth Charts

In the United Kingdom, healthcare professionals use the UK-WHO growth charts to monitor children’s development from birth through to 18 years. These charts were developed by the Royal College of Paediatrics and Child Health (RCPCH) and are based on World Health Organisation data combined with UK-specific reference data.

The charts use curved lines called centile lines (also known as percentile lines) to show the range of normal growth. There are separate charts for boys and girls, because their growth patterns differ, particularly during puberty. The key centile lines on the chart are the 0.4th, 2nd, 9th, 25th, 50th, 75th, 91st, 98th, and 99.6th.

When I see families in clinic, I always explain that the chart is not a test your child can pass or fail. It is a tool that helps us track growth patterns over time. A single measurement tells us very little; what matters is how your child’s growth progresses along or between the centile lines across months and years. If you are unfamiliar with how centile lines work, I would recommend reading our detailed guide on child weight charts and centiles in the UK.

Average Weight for Children by Age

The figures below represent the 50th centile values from the UK-WHO growth charts, meaning roughly half of UK children weigh more and half weigh less at each age. These are approximations rounded to one decimal place and should be used as a general guide rather than precise diagnostic criteria.

A few important points about these numbers. Firstly, babies typically double their birth weight by around five months and triple it by their first birthday. Secondly, you will notice that boys and girls track quite closely in weight until around age 10 to 11, when puberty begins to influence growth patterns differently. By age 16, boys on the 50th centile are typically several kilograms heavier than girls at the same centile, largely due to differences in muscle mass development.

If your child’s weight does not match these figures exactly, that is completely normal. What matters most is consistency. A child who has always tracked along the 25th centile for weight is growing perfectly well for them. To understand whether your child’s weight is in a healthy range, I recommend using a BMI calculator designed specifically for children, which takes both height and weight into account.

Average Height for Children by Age

Height (or length, for children under two who are measured lying down) follows its own growth pattern. The table below shows the 50th centile height values for UK children at key ages.

One pattern that often surprises parents is that girls tend to be slightly taller than boys between ages 10 and 12. This is because girls typically enter puberty earlier, experiencing their growth spurt sooner. Boys then catch up and overtake during their own pubertal growth spurt, usually between ages 12 and 16. By age 17, the average boy is roughly 12 cm taller than the average girl.

Height is strongly influenced by genetics. If both parents are tall, their child is likely to be above the 50th centile for height; if both parents are shorter, the child may track below. This is entirely healthy and expected. Healthcare professionals sometimes calculate a mid-parental height estimate to predict a child’s likely adult height, which can be reassuring for parents who worry about their child being shorter or taller than their peers.

Growth Differences Between Boys and Girls

Understanding the differences in growth between boys and girls helps put the numbers into perspective. In my experience, parents sometimes worry unnecessarily when comparing siblings of different sexes or when their daughter is taller than her male classmates at age 11.

During infancy and early childhood, boys and girls grow at remarkably similar rates, though boys tend to be marginally heavier and taller on average. The real divergence begins with puberty. Girls typically begin their pubertal growth spurt between ages 8 and 13, with the peak growth velocity (the fastest period of height gain) occurring around age 11 to 12. Boys enter puberty later, usually between ages 9 and 14, with peak growth velocity around age 13 to 14.

This difference in timing means that in a typical Year 6 classroom, you will often see girls who are taller and heavier than many of the boys. By Year 9 or 10, this pattern has usually reversed. These shifts are a normal part of development and do not indicate any health concerns.

Body composition also changes differently. During puberty, boys tend to develop more lean muscle mass, while girls naturally gain more body fat, particularly around the hips and thighs. This is a healthy, hormonally driven process and should not be a cause for concern or a reason to restrict a girl’s diet. If you are worried about your child’s weight during puberty, the best approach is to look at their BMI centile rather than comparing them to other children.

Centile Lines Explained: What They Really Mean

I find that centile lines cause a great deal of anxiety among parents, often because they are misunderstood. Let me clarify what they actually tell us.

A centile line shows what percentage of children of the same age and sex fall below a certain measurement. If your child is on the 75th centile for weight, it means that approximately 75% of children their age weigh less and 25% weigh more. It does not mean your child is overweight. Similarly, being on the 9th centile does not automatically mean your child is underweight.

The most important thing I look for when reviewing growth charts is the pattern over time. Healthy growth typically follows one of the centile lines, give or take a centile space. Warning signs include:

• Crossing two or more centile lines upwards or downwards over a short period
• Weight increasing rapidly while height remains static, or vice versa
• A sudden change in growth trajectory without an obvious explanation such as illness
• Weight and height centiles being very far apart (for example, weight on the 91st centile but height on the 25th)

If you notice any of these patterns, it is worth discussing them with your health visitor or GP. For a more thorough understanding of how centile charts work, our guide on understanding centiles and percentiles covers this in much greater detail.

When to Be Concerned About Your Child’s Growth

While most children grow within the expected range, there are situations where a child’s growth pattern may warrant further investigation. In my practice, I encourage parents to be observant but not anxious. Here are the key scenarios where I would recommend seeking professional advice.

Faltering growth (previously called failure to thrive): This is when a child’s weight drops across two or more centile lines, or their weight is consistently below the 2nd centile without a known reason. In young children, this may relate to feeding difficulties, food allergies, or underlying medical conditions. Early intervention can make a significant difference.

Rapid weight gain: If a child’s weight centile is climbing significantly faster than their height centile, this could indicate that they are gaining excess weight. The NHS Healthier Families programme offers free resources and support for families in this situation. You can also read our detailed guide on recognising the signs that a child may be overweight.

Very short stature: If a child is below the 0.4th centile for height, or if their height is significantly below what would be expected given their parents’ heights, further assessment may be appropriate. In some cases, this can indicate conditions such as growth hormone deficiency, coeliac disease, or Turner syndrome in girls.

Delayed or very early puberty: If a girl shows signs of puberty before age 8, or a boy before age 9, or if there are no signs of puberty by age 13 in girls or 14 in boys, this should be discussed with a healthcare professional.

I always remind parents that children do not grow in a perfectly smooth curve. Growth can occur in spurts, and minor fluctuations are normal. Illness, stress, and seasonal changes can all temporarily affect a child’s growth rate. It is the overall trend that matters.

Using BMI to Assess Children’s Weight

While weight and height tables provide useful reference points, Body Mass Index (BMI) is the measure that healthcare professionals in the UK rely on to assess whether a child is a healthy weight. BMI is calculated by dividing weight in kilograms by the square of height in metres.

Crucially, children’s BMI is interpreted differently from adults’. An adult BMI of 25 is considered overweight regardless of age, but for children, BMI must be plotted on age-specific and sex-specific centile charts. A child is generally considered:

• Underweight: below the 2nd centile for BMI
• Healthy weight: between the 2nd and 91st centile
• Overweight: between the 91st and 98th centile
• Obese (very overweight): above the 98th centile

This is why looking at weight alone can be misleading. A tall, muscular 10-year-old boy might weigh the same as a shorter, less active child of the same age, but their BMI centiles could be very different. To check your child’s BMI centile, use the NHS BMI calculator for children, which accounts for age and sex.

Data from the National Child Measurement Programme shows that in England, approximately one in five children in Reception year and around one in three children in Year 6 are living with overweight or obesity. These figures highlight why understanding and monitoring children’s growth is so important for public health.

Nutrition and Lifestyle for Healthy Growth

Healthy growth depends on a combination of good nutrition, adequate physical activity, and sufficient sleep. As a paediatric nutritionist, I see first-hand how these factors work together to support children’s development.

Balanced nutrition is the foundation. Children need a varied diet that includes all the main food groups: starchy carbohydrates for energy, protein for growth and repair, dairy or alternatives for calcium, and plenty of fruits and vegetables for vitamins, minerals, and fibre. The NHS Healthier Families programme provides excellent practical guidance on what to feed children at different ages.

Key nutrients for growth include:

• Calcium and vitamin D: Essential for bone growth and density. Children aged 1 to 18 need between 350 mg and 1,000 mg of calcium daily, depending on age. The UK government recommends a daily vitamin D supplement of 10 micrograms for all children from birth to age 4, and during autumn and winter for older children
• Iron: Supports healthy blood and cognitive development. Good sources include red meat, beans, lentils, and fortified cereals
• Protein: Needed for muscle growth and tissue repair. Most UK children get adequate protein, but quality and variety matter
• Zinc: Important for growth and immune function, found in meat, shellfish, dairy, and wholegrain cereals

Physical activity plays an equally important role. The UK Chief Medical Officers recommend that children aged 5 to 18 should engage in at least 60 minutes of moderate-to-vigorous physical activity every day. For younger children aged 1 to 4, the recommendation is at least 180 minutes of activity spread throughout the day, including active and outdoor play.

Sleep is often overlooked, but it is critical for growth. Growth hormone is released primarily during deep sleep, so children who consistently sleep poorly may not grow as well. General guidelines suggest that children aged 3 to 5 need 10 to 13 hours of sleep per night, those aged 6 to 12 need 9 to 12 hours, and teenagers aged 13 to 18 need 8 to 10 hours.

I want to emphasise that restrictive dieting is never appropriate for children unless under direct medical supervision. Children’s bodies and brains are still developing, and they need adequate calories and nutrients to support this growth. If you are concerned about your child’s weight, the focus should be on improving the overall quality of the family’s diet and increasing physical activity, not on reducing food intake. For practical guidance, see our article on what to do if you think your child may be overweight.

The National Child Measurement Programme and School Measurements

In England, the National Child Measurement Programme (NCMP) measures children’s height and weight at two key points during their school years: in Reception (ages 4 to 5) and in Year 6 (ages 10 to 11). This programme, run by the NHS, is an important part of understanding the health of the nation’s children.

After the measurements are taken, parents and carers receive a letter with their child’s results, including their BMI and what weight category their child falls into. I know from speaking with many families that receiving this letter can be stressful, particularly if the result is unexpected. If your child’s letter indicates they are above a healthy weight, try not to panic. The letter is not a judgement; it is an opportunity to take positive steps as a family.

The NCMP data also feeds into national statistics that help public health teams plan services and interventions. Recent data shows regional variations across England, with some areas having significantly higher rates of childhood obesity than others. Factors such as deprivation, access to green spaces, and the local food environment all play a role in these differences.

Scotland, Wales, and Northern Ireland have their own measurement programmes with slightly different structures, but all aim to monitor children’s growth at population level. Regardless of where you live in the UK, your child’s growth should be monitored regularly by their health visitor in the early years and through school health services thereafter.

If you would like to understand more about what happens during these measurements and what the results mean, our comprehensive guide to the National Child Measurement Programme covers everything you need to know.