Head Circumference Percentile Calculator
Compare infant head circumference to WHO growth standards for ages 0 to 5 years with percentile and z-score.
What Is a Head Circumference Percentile?
A head circumference percentile shows how an infant's head size compares to WHO growth standards for the same age and sex. Pediatricians track head growth to monitor brain development. A single reading is most useful alongside prior measurements. Compare with the Child Height Percentile Calculator and Child Weight Percentile Calculator.
WHO Head Circumference Standards
This tool uses WHO head circumference-for-age reference data from birth through 60 months. Enter age in months or years, sex, and head circumference in centimeters. The calculator returns percentile, z-score, growth band, and the WHO median for that age.
When to Consult a Pediatrician
Head circumference crossing two or more percentile lines, or readings below the 3rd or above the 97th percentile, may warrant evaluation. Rapid head growth or a plateau can signal conditions requiring imaging or specialist review. Always interpret results with your clinician.
Frequently Asked Questions
Which ages does this calculator cover?
It covers infants and young children from birth through 60 months (5 years), using WHO monthly reference data.
How should head circumference be measured?
Use a flexible measuring tape around the largest part of the head, above the eyebrows and ears, at the back where the head bulges. Enter the value in centimeters.
Can I enter age in years?
Yes. Switch the age unit to years and enter values such as 1 or 2.5. The tool converts to months internally.
What is a normal head circumference percentile?
Percentiles between about the 3rd and 97th can be normal when growth follows a consistent pattern over time. The 50th percentile is the population median.
How is the z-score calculated?
Z-score equals (measured head circumference minus WHO median) divided by the reference standard deviation at that age and sex.
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