The circumference of the head is the length of one week around the head via the top of the eyebrow arch and the posterior occipital node. It is generally about 34cm for newborns, 37~38cm at 1 month, 44cm at 6 months, 46cm at 1 year, 48cm at 2 years, 50cm at 5 years, and 54~58cm at 15 years, which is the average value and there are individual differences. Head circumference measurements are most meaningful before the age of 2 years. If the head circumference does increase, you should go to the hospital to check for hydrocephalus. Hydrocephalus is the most common cause of increased head circumference.