How to measure canthal tilt from a photo

Start with the inner and outer eye corners.

Canthal tilt describes the angle between an eye’s inner and outer corners relative to a level reference. Use the points where the upper and lower lids meet, not an eyebrow, eyeliner wing or the edge of the iris. In FaceRater’s convention, an outer corner that sits higher produces a positive angle; an outer corner that sits lower produces a negative one.

Measure the two eyes separately. Our labels use image left and image right, meaning the sides as you see them on screen. They are not anatomical left and right. Mirroring a photo swaps the screen labels, so keep the image orientation consistent when comparing readings.

Level the reference before measuring.

Level the reference for head roll first, because a tilted head can make a level eye-corner line look angled. FaceRater estimates roll from the line between the two eye centres and rotates the landmark coordinates before calculating either eye’s tilt. This is a defined reference choice, not proof that the head was perfectly positioned.

For a manual check, start with a frontal photo taken near eye level. Compare the eye-centre line with the image horizontal and account for head roll before drawing the corner-to-corner line. Leveling a picture cannot undo head turn, perspective or an obscured corner. If the face is turned noticeably, take another photo rather than trying to rescue the number.

Calculate the angle, not just the vertical difference.

After leveling, the angle in degrees is atan2(vertical rise, horizontal separation) × 180 / π, where the rise is the outer corner’s height above the inner corner and the separation is the horizontal distance between them. Use the same units for both; pixels are sufficient. Treat upward rise as positive. Image coordinates often count downward, so their raw y difference needs the opposite sign.

For an illustrative horizontal separation of 60 pixels and an outer-corner rise of 6 pixels, the angle is about +5.7°. If the outer corner is 6 pixels lower, it is about −5.7°. These are geometry examples, not suggested ideal angles. A vertical difference alone is incomplete because the same rise across a different eye width gives a different angle.

Check the test’s lines on your own photo.

Before trusting an angle, check that each corner-to-corner line ends on the real eye corners. Open the canthal tilt tool and run a free scan: it starts with the Eyes group, shows both angles and draws the lines. Follow each line to both endpoints. If a point lands on makeup, a frame or a shadow, the reading needs a better photo.

Keep the angle, image and measurement method together. Two tools can disagree because they use different landmarks or level against different references. Comparing only the numbers loses the information needed to understand that difference.

• Use one adult face looking straight at the camera.
• Keep the eye corners visible and the expression relaxed.
• Read both eyes; do not average away a difference before inspecting it.
• Check the map and any photo-quality note.
• Repeat an unclear photo under similar conditions before interpreting a small difference.

Positive and negative describe direction.

A positive angle means the outer corner sits higher and a negative one that it sits lower; a number close to zero describes an approximately level line under that measurement method. Small landmark changes can move it across zero, so FaceRater does not assign a permanent positive, neutral or negative category using an arbitrary cutoff.

A negative canthal tilt is not a diagnosis or an instruction to change your anatomy. This free tool measures a visible angle in a photograph. In the harmony score, tilt is one of two eye-area proportions, and a value in the common range or more lifted scores best; a lower tilt only lowers one of seventeen readings. If your goal is to explore your appearance, you can compare styling choices without treating the angle as something that must be fixed.