Female and Male anatomy proportions for head and torso.
The measurements are in centimeters and show the relation between the height and width of the torso with the head. The base of the head can have any size as long as the proportions keep the same.
For example, from the top of the head to the chin is one head and a half.
1 head = 2cm ; so 1,5 heads = 3cm
1 head = 4cm ; so 1,5 heads = 6cm
Also on tumblr [link]