Child BMI: Why the Number Needs a Chart
The formula is identical to adult BMI, but the interpretation is completely different. This post explains why age and sex charts exist.
What is the Child BMI Calculator?
The BMI maths is the same as for adults — weight divided by height squared — but the meaning is not. For children, the value must be plotted on an age- and sex-specific chart. This tool gives the number and the chart reminder, and it is not medical advice — check with a clinician for interpretation.
How to use it
- Enter the child's weight and height.
- Enter age and sex for the chart reminder.
- Click Calculate Child BMI.
Worked example
25 kg at 120 cm gives a child BMI of 17.36, which must be read against an 8-year-old chart, not adult bands.
Can I use adult BMI bands for a child?
No. Children's bodies change quickly with age, so a value that is typical at one age may be unusual at another.
Frequently asked questions
What chart should I use?
The growth chart used by your country's health service for the child's age and sex.
Is this medical advice?
No. It calculates a number; interpretation belongs to a clinician.