Head Percentile Calculator
Enter your child's age, sex and head circumference to get the WHO head circumference-for-age percentile, z-score and growth curve — for children from birth to 5 years.
ⓘ Educational — not medical advice. Discuss growth with your pediatrician.Calculate head circumference percentile
Uses the WHO Child Growth Standards (head circumference-for-age, 0–5 years) with the LMS method.
Years (0–5)
Months (0–11)
Total: 18 months
Measure around the widest part of the head, just above eyebrows and ears. Typical range 30–55 cm.
Result
–th
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- Z-score
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- Head circumference
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- 3rd percentile
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- Median (50th)
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- 97th percentile
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Growth curve
WHO 3rd, 50th and 97th percentile curves with your child's measurement plotted.
3rd percentile
50th (median)
97th percentile
Your child
How it's calculated
The same LMS method used by WHO and CDC growth standards. Each month of age and sex has three parameters — L (skew), M (median), S (variation):
z = ((X / M)^L − 1) / (L × S) → percentile = Φ(z) × 100
X is the measured head circumference. Φ is the standard normal cumulative distribution. Ages between monthly rows are linearly interpolated. Reference: WHO Multicentre Growth Reference Study (ISBN 9789241547185).
Scope boundary
- This tool: head circumference-for-age only, birth to 5 years (WHO standard).
- Not this tool: weight, length/height or BMI percentiles — those need their own references (see the tools directory).
- No adult mode: no validated international reference exists for adult head circumference percentiles, so none is offered.
- CDC note: the CDC charts head circumference only to 36 months; WHO 0–5 years is the broader international standard used here.
Frequently asked questions
Quick answers about head circumference percentiles.
What is head circumference percentile?
Head circumference percentile tells you how a child's head size compares with the WHO reference population of the same age and sex. A 50th percentile means the head is larger than about half of the reference children; a 10th percentile means larger than about 10%. It is a screening aid for tracking growth, not a diagnosis.
Which growth reference does this calculator use?
The WHO Child Growth Standards for head circumference-for-age (birth to 5 years), built from the Multicentre Growth Reference Study of 8,440 healthy breastfed children in six countries. It is the international standard recommended for children under five, using the LMS method: z = ((X/M)^L - 1) / (L x S), then percentile = normal CDF of z.
Why does the calculator only cover ages 0 to 5 years?
No widely validated international reference exists for head circumference beyond age 5. The CDC charts head circumference only to 36 months, and the WHO standard ends at 5 years. Extending percentiles past the reference range would be guesswork, so this tool clamps ages to 0-60 months and says so openly.
What does below the 3rd percentile mean?
It means the head circumference is smaller than about 97% of same-age children in the WHO reference. Persistently low values are sometimes followed up by pediatricians as part of microcephaly screening, which also considers the child's growth trend, development, and family pattern. A single measurement is never a diagnosis on its own.
What does above the 97th percentile mean?
It means the head circumference is larger than about 97% of same-age children in the WHO reference. Persistently high values are sometimes followed up by pediatricians as part of macrocephaly screening, alongside growth trend and development. Many children above the 97th percentile are perfectly healthy, especially with large-headed parents.
How is the percentile calculated?
With the LMS method used by WHO and CDC growth standards. Each age and sex has three parameters: L (skew), M (median), S (variation). The z-score is z = ((measurement/M)^L - 1) / (L x S), and the percentile is the standard normal cumulative probability of z times 100. Values between monthly table rows are linearly interpolated.
Are there separate charts for boys and girls?
Yes. Boys and girls have different head circumference distributions at every age, so this calculator uses the sex-specific WHO LMS tables. Select the child's sex before calculating; using the wrong table shifts the percentile noticeably.
How do I measure my baby's head circumference correctly?
Use a flexible, non-stretch measuring tape. Wrap it around the widest part of the head: just above the eyebrows and ears, around the most prominent part of the back of the head. Keep the tape snug but not tight, and measure to the nearest 0.1 cm. Measure two or three times and use the largest reading.
Can I use this calculator for adults?
No. There is no universally accepted clinical growth reference for adult head circumference percentiles, so this tool does not offer an adult mode rather than show a made-up number. It is strictly for children from birth to 5 years.
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