Child Growth Chart Calculator UK NHS

This independent UK child growth chart guide helps parents and carers work out which UK-WHO growth reference is appropriate for a child and calculate BMI from height and weight. It does not invent or approximate a centile: exact centiles require age- and sex-specific UK-WHO reference data.

What is a child growth centile?

A centile shows how a child’s measurement compares with children of the same age and sex in the reference population. RCPCH explains that a centile is the percentage expected to be below that line. Growth is best interpreted as a pattern over time, not from one measurement alone.

Which UK growth chart should be used?

RCPCH states that most children under 4 years should be plotted on the detailed UK-WHO 0-4 years chart. The UK-WHO 2-18 years chart is used for school-age children and young people. Separate charts and specialist guidance exist for very preterm babies, children needing close monitoring and children with Down syndrome.

Child BMI calculation

BMI = weight in kilograms ÷ height in metres squared. For a child, the raw BMI number must then be compared with age- and sex-specific growth reference data. Adult BMI categories must not be applied to children.

Why this page does not guess a centile

Exact UK-WHO centiles are calculated from reference data using statistical methods such as LMS. A simplified height/weight formula cannot safely reproduce a child’s centile. The NHS child BMI service uses the same data sources as the RCPCH Digital Growth Charts, so this page directs users to those authoritative services rather than generating a false centile.

How to measure accurately

RCPCH recommends appropriate weighing equipment and careful measurement. From age 2, height should be measured without shoes using a rigid rule with a T-piece or stadiometer. Measurement and age errors can affect plotting and interpretation.

Worked example

Suppose a 10-year-old child is 140 cm tall and weighs 35 kg. Raw BMI is 35 ÷ (1.40 × 1.40) = 17.9 kg/m². That number alone should not be labelled underweight, healthy weight or overweight using adult thresholds. The child’s exact age, sex and UK growth reference are needed to obtain the BMI centile.

When to seek professional advice

If you are worried about a child’s weight, height or growth pattern, contact the child’s health visitor, school nurse or GP surgery. The NHS child BMI tool should not be used to diagnose a condition. Children under 2, children with conditions affecting growth, pregnancy or suspected eating disorders require appropriate professional assessment rather than this general tool.

Authoritative sources

• RCPCH: UK-WHO growth charts 0-4 years
• RCPCH: UK-WHO growth charts 2-18 years
• NHS: BMI calculator for children and teenagers

Related calculators

NHS Calculator · BMI Calculator NHS Child · Newborn Weight Loss Calculator NHS · Baby Milk Calculator NHS · BMI Calculator NHS

FAQs

Can height and weight alone calculate a child’s centile?

No. Exact centiles depend on the child’s age, sex and the appropriate UK growth reference.

Which growth charts are used in the UK?

UK-WHO growth charts are used for children. RCPCH provides detailed 0-4 and 2-18 year charts plus specialist charts.

Can I use adult BMI ranges for a child?

No. Children’s BMI is interpreted by age- and sex-specific centiles.

Where can I get an exact child BMI centile?

Use the official NHS child BMI service or an appropriate RCPCH growth-chart service and discuss concerns with a healthcare professional.

Medical disclaimer: This independent page is for general information and growth-chart guidance only. It is not an official NHS diagnostic service and does not replace professional assessment.