Lip analysis: ratios and proportions

Lip analysis describes the size, shape, and position of the lips in proportion to the rest of the face — the ratio between the upper and lower lip, the length of the philtrum, and the width of the mouth relative to the nose and eyes. These are geometric relationships, and none of them define a single correct mouth.

The 1:1.6 upper-to-lower lip ratio

The most repeated figure in lip analysis is a roughly 1:1.6 ratio between the height of the upper lip (vermilion) and the height of the lower lip — that is, a lower lip a little over half again as tall as the upper. The number echoes the golden ratio and is often presented as an ideal.

It is worth treating as a rough average rather than a rule. It describes one aesthetic preference measured in particular populations, and real faces read as balanced across a wide band of ratios. A 1:1 ratio (equal lips) and ratios beyond 1:2 both appear frequently on faces that no one would call disproportionate. The ratio is a description, not a target.

Philtrum length

The philtrum is the vertical groove running from the base of the nose to the top of the upper lip, framed by two ridges. Its length is one of the proportions used to describe the lower face: a shorter philtrum leaves more of the upper teeth visible and tends to read as more youthful, while a longer philtrum reduces upper-tooth show. Philtrum length lengthens gradually with age, which is part of why lip proportions shift over a lifetime.

Lip width relative to nose and pupils

Mouth width is usually read against two references rather than in isolation:

• Against the nose. A classic guideline holds that the corners of the mouth sit roughly below the outer edges of the nostrils, so the mouth is a little wider than the nose base.
• Against the pupils. Another common reference places the mouth corners near verticals dropped from the centres of the pupils, tying mouth width to eye spacing.

Both are rules of thumb from artistic proportion, useful for describing where a mouth sits but not thresholds a face must meet.

How lips change with age

Lips are among the features that change most visibly over time. With age the lips tend to lose volume and the border becomes less defined; the philtrum lengthens; and the distance between the nose base and the upper lip increases, so the upper lip appears thinner and less turned outward. These changes are gradual and normal, and they shift the same proportions this page describes — which is one reason a measurement is a snapshot of a moment, not a fixed fact.

How Refrakt's AI measures lip proportions

1. Landmark location. Points are placed at the mouth corners, the two peaks and central dip of the upper lip border (the Cupid's bow), and the fullest point of the lower lip, in three dimensions.
2. Height, width, and ratio. Upper- and lower-lip heights, mouth width, and the upper-to-lower ratio are computed from those points, then normalized by face size.
3. Relative references. Mouth width is related to the nose base and pupil spacing, and philtrum length to the lower-third height, so the numbers describe proportion rather than absolute millimetres.

Why the ratio is a description, not a diagnosis

It is tempting to treat a lip ratio as a score to beat, but the measurement does not work that way. The 1:1.6 figure summarizes an average preference in specific studies; it does not predict how a particular mouth reads on a particular face. Lip proportion interacts with mouth width, philtrum length, tooth show, and the fullness of the surrounding face, so a ratio that looks balanced on one face can look unremarkable on another. A useful analysis reports the ratio and the features around it, and lets the viewer see the relationship rather than reducing it to a pass or fail.

The relationship also shifts with a smile. At rest the lips take one shape; in expression the upper lip thins, the corners rise, and tooth show increases. Because these change the very proportions being measured, a single number captured from one expression is only a slice of how a mouth actually behaves. Measuring a relaxed, neutral mouth gives a stable baseline, but it is still a snapshot rather than a fixed trait.

Cultural variation in lip ideals

Preferred lip fullness and proportion differ markedly across cultures and eras, and the research reflects this. Studies of preferred lip size find different optima in different populations, and the same measurement can be read as ideal in one context and unusual in another. Because of that, Refrakt reports lip proportions as measurements rather than scoring them against a single global standard.

Lip measurements

Commonly cited lip proportions and the references they are read against. Figures are rough averages that vary with sex, ancestry, age, and method:

Frequently asked questions