Head Circumference Percentile Calculator
Calculate a child's head circumference percentile by age and sex using WHO growth standards.
Identify normal range, microcephaly, or macrocephaly indicators.
What Is Head Circumference? Head circumference (HC) — also called occipitofrontal circumference (OFC) — is a measurement of the widest part of the head. It is measured with a flexible tape over the forehead (supraorbital ridges) and the occipital prominence at the back of the skull. Head circumference is a standard newborn and infant measurement, typically taken at every well-child visit up to age 2–3 years. It reflects brain growth — since the skull expands to accommodate the growing brain.
Why It Matters An HC below the 3rd percentile (or more than 2 standard deviations below mean) is called microcephaly. Microcephaly can indicate genetic conditions, congenital infections (Zika, CMV, toxoplasmosis), or fetal alcohol syndrome. An HC above the 97th percentile is macrocephaly. Isolated macrocephaly is often familial (benign familial macrocephaly) but can indicate hydrocephalus or storage diseases. Tracking the trend over time is more important than a single measurement.
WHO Growth Standards The World Health Organization (WHO) 2006 Multicentre Growth Reference Study established growth standards for children 0–5 years. These standards were developed from children in Brazil, Ghana, India, Norway, Oman, and the United States — all raised in healthy conditions. This calculator uses WHO reference data (mean and SD by age) approximated from published tables. For children over 3 years, CDC growth charts (2000) are the primary US reference.
Normal Development At birth: average HC ≈ 34 cm (boys) / 33.5 cm (girls). At 1 month: ~37 cm. At 6 months: ~43 cm. At 1 year: ~46 cm. At 2 years: ~48 cm. The head grows fastest in the first year — from 34 cm to ~46 cm (12 cm in 12 months). After age 2, head growth slows dramatically (only ~5 cm from age 2 to adult).
Interpreting Percentiles 50th percentile: the median — half of healthy children measure above, half below. 3rd–97th percentile: the normal range used in clinical practice. Below 3rd percentile or above 97th: warrants evaluation, not automatic diagnosis. Crossing 2 or more major percentile lines (e.g., 75th → 25th) in a short time is clinically significant.
Important Limitations This calculator provides reference percentiles for screening purposes only. Always use calibrated measuring equipment and proper technique. A pediatrician should evaluate any measurement outside the normal range or any concerning trend. Ethnic and familial variation in head size is normal.