Facial thirds

Facial thirds divide the face into three horizontal bands: hairline to glabella, glabella to subnasale, and subnasale to the bottom of the chin. The classical canon says the three should be equal, and that rule comes from Renaissance drawing instruction rather than from any anatomical finding — it is a teaching device for getting a head to look right on paper. It is still useful, because a face that departs sharply from it is departing in a describable direction: a long lower third, a short midface. The practical catch is that a landmark model cannot see a hairline, so the upper third from any photo-based tool is an estimate and everything computed from it inherits that. Our tool therefore scores only the two thirds it can actually measure — midface against lower face — and reports the upper one for what it is, an estimate from a modelled forehead rather than from your hairline.