In male pattern baldness, hair loss generally follows a path that can be tracked… not by time but by visually looking at someone. A scale was coined by Dr. James Hamilton (1950) and then updated and revised by Dr. O’Tar Norwood (1970). Since then the scale has been called the Norwood Scale or the Norwood-Hamilton Scale for male pattern baldness also known as MPB.
The scale is numbered 1-7 or I-VII and varies depending on the hair loss.
Norwood-Hamilton-Scale
Norwood I: A Norwood I has minimal hair loss or zero hair loss whatsoever. Brad-Pitt
Norwood II: This is frontal hairline and/or temporal loss that stops at 2cm in front of the ear canal and a line was drawn up to the hairline.
Norwood III: This is frontal hairline and/or temporal loss extended further back to 2cm behind the ear canal if a line is drawn from there over the top of the scalp. A Norwood IIIA is a variant that adds some hair loss in the vertex/crown area but does not exceed a Norwood III in the frontal hairline.
Norwood IV: This loss is more extensive than Norwood III and also involves more of the crown. A bridge of hair separates the frontal hairline from the vertex/crown.
Norwood V: The bridge of hair that is between the vertex/crown has shrunk in this extensive loss.
Norwood VI: In this loss, the bridge is absent completely and the hair loss is from the front to the back of the scalp.
Norwood VII: This is the highest degree of hair loss known to man and extends laterally (the sides of the head) as well as posteriorly (the crown and back of the head).
Drphil