Head Circumference Calculator (0–3 years)

With a flexible tape measure horizontally around the head — above the eyebrows at the front and over the most prominent point of the back of the head. The largest circumference counts. Ideally measure three times and average.

A percentile of 50 means 50% of same-age peers have a smaller head circumference. The 3rd–97th percentile is the normal range. Values outside are not automatically abnormal but should be checked by a paediatrician.

The fastest brain growth happens in the first three years — head circumference is the most important indicator here. After that, growth slows so much that the measurement adds little information.

A head circumference persistently below the 3rd percentile (or –2 standard deviations). Possible causes include genetic, infectious (e.g. CMV, Zika) and metabolic conditions. A single measurement is not enough for a diagnosis.

A head circumference persistently above the 97th percentile. Often familial (so-called benign familial macrocephaly) and harmless. In rare cases, hydrocephalus or a metabolic condition is the cause.

WHO Child Growth Standards 2006. These tables are based on healthy, breastfed children from six countries (Brazil, Ghana, India, Norway, Oman, USA) and are the global reference for the early years.