By Michael M. Segal MD PhD and Isabelle Rapin MD

Head circumference is measured with a tape measure extending from the middle of the forehead to the farthest part in the rear of the head, as shown in the photo.  Measurement should be done using a strong flexible tape measure, though a paper tape measure may be used until an infant has substantial hair.

Macrocephaly usually denotes a head circumference greater than the 97th percentile. Enter the head circumference in the program at the top of this page to calculate the percentile.

WARNING: Be careful about calling macrocephaly in cases in which the head size of the child is keeping to a stable percentile and one of the child's parents also has a large head without other abnormalities.