Head size, a characteristic that often sparks curiosity, reflects individual development and overall health. Understanding what constitutes an “average” head size involves considering biological factors, including how it changes from infancy through adulthood.
How Head Size is Measured
Measuring head size typically involves determining head circumference, a straightforward procedure. Healthcare professionals routinely perform this measurement for infants and young children during regular check-ups. Parents can also measure head circumference at home.
The measurement is taken with a flexible, non-stretchable tape measure. The tape is placed around the widest part of the head, usually just above the eyebrows and ears, then wrapped around the back of the head over the most prominent point. It is important that the tape lies flat against the head and that the measurement is read to the nearest millimeter.
Average Measurements by Age
Head circumference changes significantly throughout life, with the most rapid growth occurring in early childhood. For newborns, the average head circumference ranges from 34.2 to 35 centimeters (13.5 to 13.75 inches). Boys generally have slightly larger head circumferences than girls at birth, though the difference is often less than one centimeter.
During the first two years of life, a baby’s head grows at its fastest rate. For example, a one-month-old’s head circumference averages around 36.9 cm (14.53 inches). Healthcare providers use specialized growth charts from organizations like the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) to track a child’s head growth relative to typical ranges for their age and sex. These charts show how a child’s measurement compares to others.
In adulthood, head growth largely ceases, and the average head circumference stabilizes. For adult males, the average is about 57 to 57.2 centimeters (22.4 to 22.5 inches). Adult females typically have slightly smaller heads, averaging 55 to 55.2 centimeters (21.6 to 21.7 inches). Across the general adult population, head circumference commonly falls within 53 to 58 centimeters (21 to 23 inches).
Influences on Head Size
An individual’s head size is influenced by genetic and environmental factors. Genetic inheritance plays a substantial role, with specific genes contributing to head circumference variations. If parents have larger heads, their children are more likely to as well, indicating a familial component to head size.
Nutrition during developmental stages also significantly impacts head growth. Adequate nutrition, especially during pregnancy and early childhood, supports overall brain development and head size. Malnutrition, particularly during critical growth periods, can lead to a smaller head circumference.
General health conditions can also affect head size. Certain health issues or infections can influence growth patterns. Head circumference often correlates with overall body size, including height and weight.
What Head Size Reveals About Health
Head circumference serves as an important indicator of brain growth and overall health, particularly in infants and young children. Regular measurements allow healthcare providers to monitor a child’s developmental trajectory. Consistent growth along a particular percentile on a growth chart is generally a positive sign.
Deviations from typical growth patterns can sometimes signal underlying health considerations. For example, microcephaly refers to a head circumference that is significantly smaller than average, typically more than two standard deviations below the mean for age and sex. This can suggest reduced brain volume and may be associated with various neurological or cognitive developmental differences.
Conversely, macrocephaly describes a head circumference that is unusually large, also defined as more than two standard deviations above the mean. While some cases of macrocephaly are benign and familial, meaning they run in families without health issues, others can indicate conditions such as hydrocephalus, where excess fluid accumulates in the brain. Rapid increases or decreases in head circumference, rather than a single measurement, are particularly concerning and prompt further medical investigation. If there are any concerns about head size or growth, consulting a healthcare provider is always recommended.