Lip-to-chin ratio
The balance of the lower third — the upper-lip segment versus the lip-to-chin segment (classically ~1:2).
Why it matters
Lower-third balance governs how the mouth and chin relate; imbalance can look bottom-heavy or cramped.
What the lower third actually measures
The lower third of the face runs from the base of the nose (the subnasale) down to the tip of the chin (the menton). This metric does not score that whole span on its own; it looks at one internal split within it. It compares the distance from the nose base down to the lip line (the stomion, where the upper and lower lips meet) against the distance from that lip line down to the chin.
Anatomically, the upper of those two segments is mostly upper lip and the soft-tissue shelf above it; the lower segment carries the lower lip, the small labiomental fold beneath it, and the chin pad sitting over the front of the lower jaw. The tool reports the comparison as a ratio of upper to lower, so a value near 0.5 means the lower segment is about twice the upper, which is the classical 1:2 split described in anthropometric and clinical references such as Farkas 1994 and Naini 2011.
Why the split gets noticed
The eye tends to read the lower face as a short vertical stack, and the relationship between the mouth and the chin is one of the first things in that stack to register. When the upper segment grows long relative to the lower, the region between nose and mouth can look elongated and the chin a little cramped. When the lower segment dominates, the face can read as bottom-heavy. Because the mouth sits right at the hinge between the two segments, fairly small shifts change how settled or balanced the lower face appears.
It is worth being clear about what this is and is not. It is a description of layout, a proportion cue that helps explain why one lower face looks balanced and another looks long or short. It says nothing about a person, their health, or their worth.
The conventional range, and its limits
The commonly cited target is roughly 1:2, which lands near a ratio of 0.5; the tool treats about 0.44 to 0.58 as the balanced band, and faces measured on this scale tend to sit around 0.51. Two honest caveats apply. First, this is a neoclassical convention, codified by authors like Farkas and revisited in clinical practice by Naini 2011. It describes a layout that is frequently judged pleasing, not a law of beauty, and the average shifts with ancestry and sex.
Second, the segment boundaries depend heavily on lip posture. A relaxed, gently closed mouth measures differently from a slight smile or parted lips, because the lip line itself moves. The same face can therefore produce noticeably different numbers across two photos taken minutes apart.
Reading your own number sensibly
Treat the value as a position on a range, not a grade. Inside the band means the upper-lip segment and the lip-to-chin segment are close to the 1:2 convention; above or below means one of the two is relatively long. Before reading anything into it, check the photo: a level head, a relaxed and closed mouth, and a camera at eye height give the truest measurement.
The most useful thing the number tells you is directional, which segment is long, the upper lip or the lip-to-chin span. Those point to different explanations and different (mostly cosmetic-only) levers, so the direction matters more than the exact decimal.
What can and cannot change
Much of the lower third is fixed bone and soft tissue. The height of the lower jaw and the position of the chin set the lower segment, and they do not move with effort. The honest, reversible levers are about presentation: a relaxed mouth and a level head produce the most representative reading, and facial hair such as a moustache or a chin-and-jaw beard visually reweights the two segments without changing anything underneath.
Naini 2011 documents the clinical options that alter the actual proportions, including chin procedures and a surgical lip lift or genioplasty. These are medical interventions with real recovery time and risk, noted here only for completeness and not as a recommendation; any such decision belongs with a qualified specialist.
Typical range
~0.5 (1:2, lip line to chin)
Within the lower third, the nose-base-to-mouth segment (subnasale to the stomion/lip line) vs the mouth-to-chin segment (stomion to menton). About 1:2 (so ~0.5) is the common ideal.
What your reading means
- Typical
- Your lower third is well balanced.
- Less common
- Your lower-third balance is close to the 1:2 convention.
- Distinctive
- Your upper-lip or chin segment is longer than the classical balance.
How we measured it
We compare nose-base to mouth-line against mouth-line to chin.
The evidence
lowerThird.caveat
References
- Farkas, L. G. (Ed.). (1994). Anthropometry of the Head and Face (2nd ed.). New York: Raven Press.
- Naini, F. B. (2011). Facial Aesthetics: Concepts and Clinical Diagnosis. Oxford: Wiley-Blackwell.