Head Circumference Percentile Calculator

Enter your baby's age and head circumference to see their percentile on WHO and CDC growth charts. Works for infants and children from birth to age 5.

What is a head circumference percentile? A head circumference-for-age percentile compares your baby's head size to other children of the same age and sex. It is calculated using the LMS method with reference data from the CDC Growth Charts (2000) for ages 0–36 months and the WHO Child Growth Standards (2006) for ages 0–5 years. Head circumference is routinely measured at well-child visits because it reflects brain growth. Learn more about how growth percentiles work.

This tool is for informational purposes only and is not a substitute for professional medical advice. Always consult your child's pediatrician.

How Head Circumference Percentiles Work

Head circumference-for-age percentiles compare your baby's head size to a reference population of children the same age and sex. Head circumference is one of the three key measurements taken at every well-baby visit — along with weight and length — because head growth closely tracks brain development during the first years of life.

A child at the 50th percentile has a head circumference larger than 50% of children their age — this is the median. Any percentile between the 3rd and 97th is within the normal range. What matters most is that your baby's head circumference follows a consistent curve over time.

The two main reference datasets are:

This calculator shows both charts side by side when the age falls within both datasets' ranges.

Why Head Circumference Matters

Pediatricians monitor head circumference because it's a reliable indicator of brain growth. A head that's growing too quickly (macrocephaly) or too slowly (microcephaly) may signal conditions that benefit from early intervention. However, head size varies widely among healthy children, and many babies with large or small heads are perfectly healthy — especially when the measurement tracks consistently along the same percentile curve.

Head Circumference FAQ

How do I measure my baby's head circumference?
Wrap a flexible, non-stretchy measuring tape around the widest part of your baby's head — above the eyebrows, above the ears, and around the most prominent part of the back of the head (the occiput). Take three measurements and use the largest. See our full measurement guide.
What is a normal head circumference percentile?
Any percentile between the 3rd and 97th is within the normal range. A baby at the 15th percentile is just as healthy as one at the 85th — what matters is that the measurement tracks consistently along the same curve over time rather than crossing multiple percentile lines.
When should I worry about my baby's head size?
Talk to your pediatrician if your baby's head circumference is below the 3rd percentile (microcephaly), above the 97th percentile (macrocephaly), or if the measurement has crossed two or more major percentile lines over several visits. A single reading outside the typical range is rarely cause for concern on its own — head size is partially genetic.
Why is head circumference measured at well-baby visits?
Head circumference is measured routinely because it reflects brain growth. The brain grows rapidly in the first two years of life, and tracking head size helps pediatricians detect conditions like hydrocephalus (fluid buildup) or craniosynostosis (premature skull fusion) early, when intervention is most effective.
Does a large head mean a smarter baby?
No. While head circumference correlates with brain volume, there is no reliable relationship between head size and intelligence within the normal range. Many factors influence cognitive development, and head circumference is primarily used to screen for medical conditions, not predict intelligence.
What is a z-score for head circumference?
A z-score measures how far your baby's head circumference is from the median in standard deviation units. A z-score of 0 means exactly at the 50th percentile. A z-score of +2 is roughly the 98th percentile, and −2 is roughly the 2nd percentile. Clinicians often use z-scores because they're more precise at the extremes.