Chin-to-philtrum ratio

More space above the upper lip separates the mouth from the nose. More space below the lower lip extends the chin region. Their relative heights help describe whether the mouth sits high or low within the lower face.

The visible lips lie between these intervals and are excluded from both. A tall lip pair can therefore occupy substantial space even when the surrounding skin intervals are short. Keep the lip borders visible when reading the figure so the chin segment is not confused with the full distance below the mouth seam.

A short philtrum raises the ratio by placing the upper lip close beneath the nose. The chin interval may remain ordinary, leaving a compact nose-mouth relationship with more space below the lips than above them.

A tall chin segment raises the ratio through extra height beneath the lower lip. The mouth may remain at a similar distance from the nose while the lower face extends downwards. With a broad chin, this can create a substantial rectangular base; with a narrow chin, it can produce a more elongated finish.

These features can occur together, but a high ratio does not require a long lower face. A short philtrum and moderate chin interval may share the ratio of a much taller arrangement. Lower-third height shows which overall scale surrounds the lips.

A longer philtrum moves the upper lip farther below the nose. If the chin segment does not extend similarly, the mouth sits lower within the available space and the skin above it becomes more noticeable.

A short chin interval also lowers the ratio while the philtrum stays the same. The lower lip then sits close to the bottom of the face. This may create a compact lower region rather than an elongated upper-lip region.

Lip height affects both appearances. Full lips occupy more of the space between the measured intervals, while limited visible lip height makes the surrounding skin more conspicuous.

A high ratio in a long lower face is more likely to involve appreciable height below the mouth than the same ratio in a short lower face. Chin width then changes the shape of that height. A broad, tall chin can continue a wide jaw, while a narrow, tall chin creates a finer extended section beneath the lips.

Philtrum-to-lower-third ratio compares the upper interval with the full nose-to-chin height. The measurements are related but not exact inverses: the full lower third includes the visible lips, whereas chin-to-philtrum excludes them. A change in lip height can affect the full allocation without changing the two surrounding intervals in the same way.

Forward chin projection requires a side view. A broad, tall frontal chin may still sit relatively far back in profile, while a narrower chin may project clearly.

The skin above the upper lip has a central groove and raised borders that affect how its length is perceived. Nunes and Bran found that removing philtral definition in edited portraits made the region appear longer and older to many observers, without physically lengthening it.

A clearly defined philtrum above a full upper lip may consequently look different from the same measured interval above a small upper-lip display. The contour and the visible lip border help explain why the ratio does not always match the impression of nose-to-mouth distance.

The lower face grows substantially towards adulthood, which can add height below the lips alongside changes in jaw breadth. A higher ratio may arise as part of this wider development rather than through shortening above the mouth.

Later changes in visible lip height and philtral definition affect the appearance of the surrounding intervals. Sforza and colleagues documented declining vermilion measures with age. Comparing older photographs can help distinguish a longstanding proportion from a change in lip display or the skin above it.

The 2.0–2.5 reference describes a chin interval roughly twice to two and a half times the philtrum height. Studies that begin the lower interval at the mouth seam include part of the lips and produce a different ratio, so their numerical values need separate interpretation.

Naini and colleagues found tolerance across a range of chin heights in their experiment. That result concerns the height they changed rather than this exact ratio, which can also move through a change in philtrum length.