Mouth-to-interpupillary width ratio

The eyes establish a horizontal span above the mouth. When the mouth corners sit well inside the pupil lines, the lower centre looks narrower than the upper span. As mouth width approaches pupil spacing, the lips occupy more of that width below the eyes.

The mouth can change in relation to the eyes while keeping the same proportion to the nose. This makes the pupil comparison useful when a nose-mouth pair looks proportionate locally but small or broad beneath the eye region.

A low ratio may come from a narrow mouth beneath ordinarily spaced eyes. If mouth-to-nose width is low too, with a modest nasal base, the mouth has a restrained span against both neighbours. Full lips can still give that narrow mouth substantial visible presence.

Widely spaced pupils also lower the ratio around a mouth of ordinary width. Long eyes or a large inner gap may contribute to that upper span. In this case, the eye arrangement makes the mouth look narrow by comparison.

A high ratio can similarly reflect a broad mouth or closely spaced pupils. If both mouth width and pupil spacing increase together, their proportion can stay stable while the central features occupy more of the face.

Pupil-to-face width helps determine whether the eye span is broad within the cheeks. A high value alongside a low mouth-to-pupil ratio makes wide eye spacing a plausible contributor. If the mouth remains substantial beside the nose, the result may describe a broad eye region rather than a small mouth.

When the mouth is narrow against both pupil spacing and a modest nasal base, its own width contributes more clearly. At the opposite end, a mouth broad against both references has greater horizontal reach through the lower centre. Compare lip height as well: a wide, thin mouth and a narrower, full mouth distribute their visible area differently.

Narrowing pupil spacing raises mouth-to-pupil width without changing the lips.

The same mouth width can sit close beneath the eyes or much farther down. A short eye-to-mouth distance groups the spans into a compact centre. More height separates them and gives the arrangement a deeper shape, even when their widths stay unchanged.

Eye-to-mouth angle describes this depth relative to pupil spacing. The philtrum then shows how much of the space immediately above the mouth lies below the nose. A long philtrum separates the lips from the nasal base, while more height below the lower lip places the mouth higher within the lower face.

The 72–84% reference describes a mouth spanning roughly three quarters to just over four fifths of pupil separation. The corners remain inside the pupil lines while providing a substantial lower horizontal span.

Pallett and colleagues found that changes in eye and mouth placement affected attractiveness ratings. Torsello and colleagues documented departures from classical proportions in selected female models. Neither study establishes a preferred range for this width ratio.

The mouth and eye region follow different growth schedules, so their relative widths can change during maturation. Adult lip changes can alter the comparison again. Sforza and colleagues documented age-related differences in mouth width and declining visible lip height relative to width.

A rising mouth-to-pupil ratio may therefore accompany a less vertically full mouth. Expression introduces a temporary change too: smiling moves the corners outward, while gaze shifts the pupils within the openings. Relaxed lips and direct gaze make the resting comparison more consistent.