While numerous charts detailing head sizes in infants and children exist, most do not measure average head circumference past the age of 21. Reference charts for adult head circumference also generally feature homogeneous samples and fail to take height and weight into account.

One study in the United States estimated the average human head circumference to be 55 centimetres (21 3⁄4 in) in females and 57 centimetres (22 1⁄2 in) in males.]

An English study showed an average size of 55.2 cm for females and 57.2 cm for males with average size varying proportionally with height

Wright et al tested whether different measuring techniques produce systematic differences in head size that could explain the large head circumferences found in Northern European children compared with the WHO standard.

The WHO measurement techniques produced significantly lower measures of head size, but average healthy Scottish children still had larger heads than the WHO standard using this method ¹⁾.