Chin-to-philtrum ratio: chin height explained

What chin-to-philtrum ratio is

The philtrum is the groove between the base of your nose and your upper lip. The chin-to-philtrum ratio compares the height of your chin, from the lower lip to the tip of the chin, with the height of that groove. A larger value means a taller chin compared with a short philtrum.

This is one of the measures where the camera angle and expression matter most, because a smile shortens the philtrum and a tucked chin shortens the chin. The ratio is helpful as a guide to chin presence and beard choices, and is less decisive than it sounds.

In the LookFlex app this measurement appears as Chin-to-philtrum.

How LookFlex measures it

LookFlex measures the vertical distance from the bottom of the lower lip to the tip of the chin, then the vertical distance from the base of the nose to the top of the upper lip, and divides the first by the second. Vertical distances are sensitive to head nod, so the face is levelled and corrected first.

On the face mesh the philtrum reads shorter than it looks, which pushes the ratio higher than textbook figures. LookFlex's ranges are set in the mesh's own units for that reason.

The calculation: ratio = (lower lip to chin tip) ÷ (nose base to upper-lip top).

Landmarks used

LookFlex reads these points from the 478-landmark face mesh. The numbers are each point's index in that mesh.

• Bottom of the lower lip: 17
• Tip of the chin: 152
• Base of the nose: 2
• Top of the upper lip: 0

The full pipeline, including how pose and mirror-averaging reduce noise, is on how LookFlex measures your face.

Typical and scoring ranges

LookFlex shows two ranges. The typical range is the middle half of its reference set, from the 25th to the 75th percentile: half of the faces fell inside it. The scoring range is where a reading earns a closeness score of 100; outside it the score falls smoothly, with no cliff at the edge. Both differ for men and women, and LookFlex blends the two if you choose Other or prefer not to say. Unit: unitless ratio.

How to read your result

"The range" here means the scoring range. The impressions below are common styling descriptions, not research findings. What research does show is in the next section.

• Below the range: A shorter chin relative to the philtrum. A short beard is a common way to add visual height.
• Inside the range: Chin and philtrum sit inside the scoring range.
• Above the range: A tall chin relative to the philtrum: a prominent, defined lower face.

What the research says

Limited evidence We found no study of this proportion, so it rests on styling convention.

• Real faces vary widely in their proportions (Farkas et al., 1985).
• Judgments of character from faces are often inaccurate, so chin size should not be read as character (Todorov et al., 2015).
• LookFlex's range is calibrated on its own reference set and is not drawn from a published norm.

No study we cite tests LookFlex's own ranges. They come from the calibration described on the methodology page, and every source is listed under References below.

What influences it

Mostly fixed

• The height of the chin bone and the length of the upper lip, both set by genetics.
• Age, which can change the upper lip and philtrum.

Things that move the reading

• Expression. A smile pulls the upper lip up and shortens the philtrum, raising the ratio.
• Head pitch. A tucked chin shortens the visible chin, a lifted chin lengthens it.
• Facial hair. Stubble or a short beard adds visual height to the chin.
• Posture, in particular a forward head position, which can hide the chin line in photos.

How to improve how it reads

These suggestions change how the measurement reads or how well the photo captures it. Styling tips are common practice rather than tested in research, and none of them promises a change in bone structure.

• Scan with a closed, relaxed mouth and a level head.
• A short, well-shaped beard or stubble below the lip extends the visual height of a shorter chin.
• When you scan, keep your head stacked over your shoulders with the chin neither jutting nor tucked.
• If fat under the chin hides your chin line, body composition is the lever (Coetzee et al., 2009). Aim for gradual change through training and food; LookFlex does not recommend crash diets.

Common myths

Myth: A small chin means a weak character.

Judgments of character from faces are often inaccurate (Todorov et al., 2015), so chin size should not be read as character. It is a proportion that affects the profile, and beards, haircuts and posture can all balance it.

Myth: Chin exercises or tongue posture can build a chin.

We found no reliable evidence that exercises or tongue position change adult bone structure. LookFlex does not recommend them as a way to alter your chin.

How it feeds your score

This measurement is one input to 2 sub-scores, which then combine into your Glow Score:

• Jawline: 15% of the sub-score. Jawline carries 17% of the Glow Score.
• Harmony: 10% of the sub-score. Harmony carries 22% of the Glow Score.

Precision. Every reading of this measurement comes with a 95% margin, estimated by measuring your photo three times. Across the reference set the median margin was ±0.17: a retake in similar conditions usually lands within that much of the first reading. A change between two scans counts as real only when it is bigger than both scans' margins combined.

Confidence. LookFlex starts this measurement at a confidence of 75% and lowers it when your head angle, the lighting or image quality weakens the reading. The weight of each input in a sub-score scales with its confidence. Details are on the methodology page.