Child height, weight and BMI calculator (WHO percentiles)
Enter your child’s sex, age, height and weight — the calculator returns percentiles and z-scores from the World Health Organization standards (separately for boys and girls) and shows whether height, weight and BMI fall within the age norm. A percentile is not a diagnosis but where your child sits among peers; a doctor assesses development.
Calculate your child’s height, weight and BMI percentiles
Enter sex, age and at least height or weight — the result appears instantly.
How to read a percentile
A percentile shows how many children of the same sex and age have a lower value. The norm is a wide band; the trend along your child’s own curve matters more than a single point.
| Percentile | What it means |
|---|---|
| below 3rd | Well below average — show a paediatrician |
| 3rd–15th | Below average, often a normal variant |
| 15th–85th | Within the norm (middle band) |
| 85th–97th | Above average, often a normal variant |
| above 97th | Well above average — show a paediatrician |
What a percentile and z-score are
A percentile shows what share of children of the same sex and age are shorter or lighter than your child. The 50th percentile is the median (the middle): half of children are below, half above. The z-score is the same thing in standard deviations: 0 is the median, −2 and +2 are the usual limits of the norm (roughly the 3rd and 97th percentiles).
The norm is a wide range — about the 3rd to the 97th percentile. A child on the 10th percentile isn’t “behind”: they’re simply below average, which may be their build. What matters is not a single point but how the child stays on their own curve over time.
Where the norms come from: WHO standards
The calculator uses the WHO Child Growth Standards (0–5 years) and the WHO reference for 5–19 years — international tables built with the LMS method separately for boys and girls at each month of age. From the L, M and S parameters for a given age and sex it computes a z-score for the measurement, and from that the percentile.
We report three indicators: height-for-age (short/tall stature), weight-for-age (WHO defines it up to 10 years) and body mass index for age (underweight, overweight, obesity). A child’s BMI is judged by age percentiles, not by the “adult” 18.5–25 band.
Predicting adult height from the parents
A rough adult height can be estimated from the parents’ heights (mid-parental height, Tanner method): for a boy — (father’s + mother’s height + 13 cm) / 2, for a girl — (father’s + mother’s height − 13 cm) / 2. The typical spread around this figure is about ±8.5 cm.
It’s a rough prediction: real height depends on nutrition, health, hormones and the timing of puberty. Enter the mother’s and father’s heights in the “Refine for you” block to see the estimate.
When to show your child to a doctor
See a paediatrician if a value is below the 3rd or above the 97th percentile, or if the child sharply crosses percentile bands (for example, long on the 50th and then quickly dropping to the 15th or jumping to the 85th). Sitting near the edge of a band with a stable trend and good wellbeing is usually a normal variant. The calculator is a guide, not a diagnosis.
Decode your child’s tests
Upload your child’s tests — AI explains the values for their age and points out what to watch.
This calculator is for reference and information only and shows WHO percentiles. It is not a diagnosis: a paediatrician assesses a child’s development by trend, examination and tests.