The head circumference of a normal adult is 54 to 58cm, and that of a newborn is usually about 34cm, about 46cm at the age of 1 year, about 48cm at the age of 2 years, and close to that of an adult at the age of 15 years. The standard of head circumference is different at different ages, generally in early childhood, the measurement of head circumference has some significance. The head circumference of a newborn baby is usually around 34cm, but the fontanel of the newborn baby is not yet closed. With age, the baby’s head gradually develops, the fontanel closes and the head circumference grows. The head circumference is usually around 46cm at the age of 1 year and 48cm at the age of 2 years. If the head circumference is too small, it may indicate microcephaly, and if the head circumference is too large, it may indicate hydrocephalus and rickets. Generally, the head circumference is about the same size as that of an adult at the age of 15 years, and will not change significantly. It is recommended to go to the hospital for examination if you find any abnormality in the size of head circumference.