cephalic index (səfălˈĭk) [key] [Gr. kephale = head], ratio of the breadth of the head to its length. Expressed as a percental number, it provides the simplest description of the geometric relation of two dimensions. The index is obtained by dividing the maximum width of the cranium by its maximum length and multiplying by 100. In anthropometry, the cephalic index has been the favored measurement. A cephalic index of 80 or more is called brachycephalic or broad; a measurement between 75 and 80 is mesaticephalic; below 75 is considered dolicocephalic or long. The cranial index is the same ratio taken on a skull.