WHO Child Growth Standards
Head Circumference Percentile Calculator
Use one dated head circumference measurement to calculate a WHO head-circumference-for-age percentile and z-score for a baby from birth through the day before the second birthday.
This focused page uses the actual birth date, measurement date, and selected WHO boys or girls chart. The result is a reference comparison for one measurement, not a diagnosis or growth trend.
For weight, recumbent length, or several WHO indicators together, use the Baby Growth Percentile Calculator.
What this percentile means
A head circumference percentile shows where the submitted measurement falls on the WHO reference distribution for the selected sex and exact age. Percentiles are reference positions, not targets, normality labels, or treatment goals.
A single result does not diagnose microcephaly, macrocephaly, hydrocephalus, developmental delay, or another neurological condition. Clinical interpretation uses reliable measurements over time and the child's broader context.
How to measure head circumference correctly
- Use a narrow, non-stretchable tape.
- Place it above the eyebrows, above the ears, and around the most prominent back of the head.
- Keep the tape level and snug without compressing the skin.
- Repeat an uncertain reading and record the largest reliable circumference to the nearest 0.1 cm.
Why exact age and measurement accuracy matter
The WHO reference changes across infancy, so the calculator uses the actual birth date and measurement date to select an exact integer age-day row. Tape placement, tension, posture, movement, unit entry, and date errors can change the reference comparison.
One measurement versus a growth pattern
This page answers a one-date question. Repeated, accurately dated measurements are needed to evaluate a pattern. A later measurement can be calculated again, but this page does not produce a velocity percentile or a prediction.
What this calculator cannot diagnose
The output is a WHO reference comparison. It cannot diagnose a neurological condition, developmental delay, hydrocephalus, microcephaly, macrocephaly, or any other disease, and it does not provide treatment or feeding advice.
A technical WHO extreme-value flag only prompts a careful measurement review. It does not replace the percentile or label the child.
Head circumference versus the full Baby Growth Calculator
Use this focused page when the task is one head circumference. Use the Baby Growth Percentile Calculator when you have weight, recumbent length, head circumference, or a combination and want the four WHO indicator results together.
Preterm babies and corrected age
For babies born preterm, chronological age may not be the age basis used for every clinical growth assessment. This calculator does not automatically apply corrected age or choose a preterm growth chart. The Corrected Age Calculator provides a timeline only; an appropriate healthcare professional should confirm the chart and age basis.
Why this calculator stops at age 2
The WHO head-circumference-for-age data used here covers birth through the day before the second birthday. This focused page ends at that boundary, and Child Growth Lab does not currently provide a head-circumference percentile calculator for age 2 or older.
For head circumference after the second birthday, use a reference appropriate to the clinical setting with an appropriate healthcare professional. If the task is an age-2-or-older height, weight, or BMI comparison, use the Child Growth Chart Calculator; it does not calculate head circumference. This page does not extend the WHO infant scope to ages 2–5.
Worked example
A girl born January 1, 2026 and measured February 20, 2026 is 50 days old. A head circumference of 37.6 cm produces a result of about the 46th percentile with a z-score of about −0.09 on the WHO girls head-circumference-for-age reference.
The example is a reference position, not a target, healthy-size label, diagnosis, or growth trend.
How the calculation works
The calculator uses the actual birth date, measurement date, exact integer age in days, selected WHO sex chart, and the existing WHO head-circumference-for-age LMS table. The base WHO LMS transformation produces the z-score and percentile; no monthly approximation or separate head-circumference algorithm is used.
The licensed WHO table, provenance checksum, permission record, and validation details remain inspectable in the collapsed technical section and Methodology.
Limitations
- The scope is birth through the day before the second birthday.
- Child Growth Lab does not currently provide a head-circumference percentile calculator for age 2 or older; an appropriate clinical reference and healthcare professional are needed for that context.
- The calculation uses chronological age and does not automatically apply corrected age or select a preterm chart.
- Results depend on accurate dates, units, selected sex chart, and repeatable head circumference technique.
- The result is a screening reference position, not a diagnosis, treatment recommendation, or complete developmental assessment.
- The page does not save measurements, create profiles, or calculate a longitudinal record or velocity percentile.
Sources
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- 7WHO Child Growth Standards data used under WHO Permission Request 202609680, granted 2026-07-16.
No WHO logo is used. Child Growth Lab is independent and is not affiliated with or endorsed by WHO. WHO data remain within the permitted website/software calculator and are not offered as a standalone download.
Helpful context
Frequently asked questions
What is a head circumference percentile?
It is a reference comparison between one head circumference measurement and the WHO head-circumference-for-age distribution for babies of the same sex and exact age. It is not a diagnosis or a target.
How accurate is a head circumference measurement?
Accuracy depends on tape position, level, tension, and repeatability. Use a narrow non-stretchable tape, place it around the maximum occipitofrontal circumference, repeat an uncertain reading, and record the largest reliable value to the nearest 0.1 cm.
How do I measure my baby’s head circumference?
Place the tape above the eyebrows and ears and around the most prominent back of the head. Keep it level and snug without compressing the skin, then repeat the measurement if needed.
Does a low or high percentile diagnose a condition?
No. A single percentile does not diagnose microcephaly, macrocephaly, hydrocephalus, developmental delay, or another neurological condition. A reliable series and clinical context are important.
Why does exact age matter?
The WHO reference changes across infancy. Using the actual birth date and measurement date selects the integer age-day row rather than a rounded month estimate.
Does this calculator use corrected age for premature babies?
No. It uses the actual birth date and chronological age and does not automatically apply corrected age or select a preterm chart. Use the Corrected Age Calculator for a timeline and confirm the chart and age basis with an appropriate healthcare professional.
Why does this calculator stop at age 2?
This focused page ends before the second birthday. Child Growth Lab does not currently provide a head-circumference percentile calculator for age 2 or older. For head circumference after that point, use a reference appropriate to the clinical setting with an appropriate healthcare professional. If you need age-2-or-older height, weight, or BMI, use the Child Growth Chart Calculator; it does not calculate head circumference.
How is this different from the Baby Growth Percentile Calculator?
This page focuses on one dated head circumference. The Baby Growth Percentile Calculator can combine weight, recumbent length, weight-for-length, and head circumference in one WHO review.
Does Child Growth Lab save the measurement?
No. The calculation runs in this browser. Inputs are not saved as a child health record and are not sent to an external calculation service.
Understand this result
What Do Baby Growth Percentiles Mean?
Understand WHO head-circumference, weight, length, and weight-for-length percentiles before age 2 and what one result can and cannot show.