Lip ratio: lower lip versus upper lip

What lip ratio is

Lip ratio compares the height of your lower lip with the height of your upper lip. A classic balance is a lower lip somewhat taller than the upper, and a ratio of about 1.5 is often quoted. A value near 1.0 means the two lips are equal in height, and values above 2.0 mean the lower lip is much fuller.

Lips are a small area with a large effect on the face's character, and they change with hydration, expression and light. The ratio is best used as a gentle guide to makeup, grooming and how your lips appear in photos.

In the LookFlex app this measurement appears as Lip balance.

How LookFlex measures it

LookFlex measures the height of the upper lip, from the top edge to the line where the lips meet, and the height of the lower lip, from that line to the bottom edge, and divides the lower by the upper. Because the measure is a pure ratio of two heights, it does not depend on image size.

Pressed or pursed lips hide the red part of the lip and shift the ratio, and so does a smile that stretches the upper lip thin. A relaxed, closed mouth is the most reliable pose.

The calculation: ratio = lower-lip height ÷ upper-lip height.

Landmarks used

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

• Top of the upper lip: 0
• Line where the lips meet: 13, 14
• Bottom of the lower lip: 17

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. The scoring range is the same for everyone, while the typical range follows each group's own median. 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: The upper lip is relatively full: a soft, pouty balance.
• Inside the range: A lip ratio inside the scoring range.
• Above the range: The lower lip is notably fuller: a bold balance.

What the research says

Limited evidence The popular golden-ratio claim for lips is not supported; no study sets an ideal lip ratio.

• The popular golden-ratio face mask fits many faces poorly (Holland, 2008), and we found no study supporting a 1.618 lip ratio.
• Real faces vary widely in their proportions (Farkas et al., 1985).

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 shape and volume of the lips, which are anatomical and inherited.
• Age, which can change lip volume.

Things that move the reading

• Hydration and dryness. Dry or flaky lips blur the lip line and change the measurement.
• Expression. Tension, a smile or pressed lips all change visible lip heights.
• Lip colour, liner and balm, which change how the lips read.
• Sun exposure, which can dry the lips.

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.

• Use a balm with SPF 30 or higher in daylight, and keep lips hydrated.
• If you exfoliate, be gentle. A soft cloth after brushing is enough.
• Use liner or colour that follows your natural line to rebalance how the lips read.
• Scan with a relaxed, closed mouth and a neutral face.
• Avoid DIY plumping tools and injections. If you want a change, discuss it with a board-certified professional.

Common myths

Myth: There is a golden-ratio lip proportion everyone should have.

The idea that a lower lip should be exactly 1.618 times the upper is a popular claim. A well-known golden-ratio facial mask fits many faces poorly (Holland, 2008), and we found no study supporting a 1.618 lip ratio. LookFlex's range is 1.40–2.00, which spans the typical values in its reference set up to a fuller lower lip.

Myth: Fuller is always better.

Fuller lower lips are the preferred direction in the conventions LookFlex uses, but proportion, colour and expression matter at least as much.

How it feeds your score

This measurement is one input to one sub-score, which then combine into your 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 ±0.10: 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.