The standard for normal adult head circumference is 53 cm or more. The size of the head is measured by head circumference, which is measured with a soft ruler from between the eyebrows around to the back of the head and through the occipital ridge. The change in head circumference during the developmental stage is about 34 cm for newborns, increasing by 8 cm in the first six months after birth, 3 cm in the second six months, 2 cm in the second year, 1.5 cm in total in the third to fourth years, and about 1.5 cm from 4 to 10 years of age. 53 cm or more can be reached after 18 years of age, and almost no change thereafter. Cephalic abnormalities in adults are mainly seen in patients with Marfan’s syndrome, acromegaly, and deformational osteitis.