Lower-to-upper lip ratio

The coloured surface of the lips is called the vermilion. Its upper and lower borders enclose the measured heights on either side of the mouth seam. The skin between the nose and upper lip belongs to the philtrum and is outside this comparison.

The ratio describes how height is distributed, so equal thin lips and equal full lips can share a result. Looking at their combined height relative to mouth width shows whether the pair is full or slender before considering which lip contributes more.

A high ratio can come from a substantial lower lip beneath an appreciable upper lip. The mouth looks fuller below the seam while the upper lip retains a clear presence. A small upper-lip display can produce the same ratio beneath a more moderate lower lip, without adding fullness overall.

At a low ratio, a tall upper lip creates more visible area above the seam. A small lower lip can also lower the result, but the mouth may remain relatively thin. Inspect both heights before treating either direction as evidence of greater fullness.

If both lips become taller in the same proportion, their ratio remains stable while the mouth gains visible area.

The upper lip's Cupid's bow can make its border distinct even with modest central height. Fullness towards the sides also changes the lip's area without an equivalent change at the centreline. Similar central ratios can consequently belong to different contours across the mouth.

Mouth width determines how that height is spread. A narrow mouth with tall lips concentrates the visible area, while the same heights across a wider mouth create a more elongated shape.

Forward projection adds another dimension. A lip can turn outward and expose more surface, or project in profile while showing modest frontal height. Visible vermilion height measures the surface presented to the camera rather than tissue volume.

A full lower lip beneath a substantial upper lip can form a compact nose-mouth region when the philtrum is short. A high ratio caused by little upper-lip display beneath a long philtrum creates a different effect: more skin is visible above the mouth while the upper lip occupies less space.

The chin determines how much height remains below the lips. A tall chin can make the same lip pair look smaller within the lower face, while a short chin places more of the visible area around the mouth. Chin-to-philtrum and philtrum-share measurements help locate the lips within those surrounding intervals.

Nasal width supplies a nearby horizontal comparison. A narrow but full mouth can remain prominent beneath a broad nasal base. A wide mouth with thinner lips may extend far beyond the nose without looking equally full.

Popenko and colleagues varied lip area and upper-to-lower proportions in female facial images. A lower lip approximately twice the upper was preferred within their experiment, where total projected lip area was considered alongside the proportion.

Heidekrueger and colleagues used altered versions of one female face in a survey of 1,011 respondents across 35 countries. About 60% selected equal upper and lower proportions. The available alternatives differed from Popenko's experiment, as did the underlying faces and rating tasks.

The 1.5–1.8 reference describes a visibly taller lower lip. Neither experiment established this interval as a preferred range.

Sforza and colleagues documented increases in vermilion measures into adolescence, followed by declines in several measures with age. If upper and lower lip heights change proportionately, the ratio can remain similar while their total display decreases. If one changes more, the ratio shifts as well.

Changes in philtral definition can alter the impression around the upper lip without changing its measured height. Nunes and Bran found that reduced definition made the region above the mouth appear longer in edited portraits. This can make limited upper-lip display more noticeable alongside the same lower lip.

Use relaxed, gently closed lips for comparison. Pursing, smiling or separating them changes the displayed heights and may move the central seam.