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Head circumference percentile calculator

Enter your child’s age, sex and head measurement to see where it falls on the WHO and CDC growth charts.

Head circumference percentile calculator

Sex

Enter the head circumference to see the percentile.

Data: WHO Child Growth Standards (0 to 24 months) and CDC growth charts (24 to 36 months).

What the percentile means

A percentile compares one measurement with a large reference group of healthy children of the same age and sex. A baby on the 60th percentile has a larger head than 60 out of 100 babies of the same age. Percentiles between roughly the 3rd and the 97th are considered within the typical range.

Where the data comes from

From birth to 24 months the calculator uses the WHO Child Growth Standards, which the WHO and the CDC recommend for this age. From 24 to 36 months it uses the CDC 2000 growth charts. It applies the LMS method published with each chart to turn a measurement into a z-score and a percentile.

Following the curve

A single percentile says less than the pattern over time. Most babies stay near the same percentile line. A measurement that crosses two major percentile lines, or sits below the 3rd or above the 97th, is worth discussing with a doctor.

How to measure your head

  1. 1 Use a soft tape measure, or a string and a ruler.
  2. 2 Wrap it around your head where the hat will sit: about 1 cm (⅜ in) above your ears and across the middle of your forehead.
  3. 3 Keep the tape level and snug, not tight. Do not pull it in.
  4. 4 Read the number where the tape overlaps. Measure two or three times and use the largest value.
  5. 5 Type the number into the calculator, or find it in the chart.
How to measure

Frequently asked questions

What is a normal head circumference percentile?

Anything from about the 3rd to the 97th percentile is within the typical range. Doctors pay most attention to changes over time.

Is the 90th percentile for head circumference bad?

No. It means the head is larger than 90 out of 100 children of the same age and sex, which is within the typical range.

What does the z-score mean?

It is the number of standard deviations from the median. A z-score of 0 is the median, and scores of about −2 and +2 correspond to the 2nd and 98th percentiles.

Can I use this calculator for older children?

It covers birth to 36 months. For older children, see the typical ranges on the head circumference by age page.

Related charts

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