At birth, the average newborn’s head circumference measures approximately 13 3/4 inches and grows to around 15 inches during the first month, according to the American Academy of Pediatrics. Newborn boys often have slightly larger heads than girls. The difference is typically less than 1/2 inch.
Since head growth mirrors the growth of the brain, pediatricians closely monitor growth progress in infants and young children. The bones continue fusing together during the early months of an infant’s life. The head and skull grows faster than at any other time in life during the first four months, notes the American Academy of Pediatrics.