Size of Head: The distance from the chin to the crown is the same as from the back of the head to the front. The mid-point of the face, when measured from chin to crown, is at the base of the eyes or eye sockets.Eyes: The space between the eyes is about the same width as one eye. If the width of eye is used as a unit of measurement, the head is five eyes wide.
Eyebrows: Extend beyond the eyes on both sides.
Ears: The top of the ears line up with the brow of the nose and the eyebrows, and the bottom of the ears with the tip of the nose.
Nose: The bottom of the nose is the midpoint between the eyes and the chin.
Mouth: The corners of the mouth align with the center of the eyes (if you're not smiling). The line where the two lips meet is slightly above the halfway point between the end of the nose and the chin.
Chin: The mound of the chin starts at the inner corners of the eyes.
from: http://www.drawspace.com/lessons/h01/horizontal-facial-proportions-of-adults and http://painting.about.com/od/figuresportraits/ss/figure_class_2.htm
