Guide · Updated 2026-10-08
How Face Shape Detection Works (and How Reliable It Is)
How a face shape detector measures landmarks, turns them into ratios and picks oval, round, square, heart, diamond or oblong, and why the result is only an estimate.
Face shape tools are popular for choosing glasses and haircuts. Underneath, they all do the same thing: measure a few distances on a face and compare the ratios with rules. This guide explains how the Face Shape Detector does it, so you know how much weight to give the answer.
Step 1: find the face
A face-landmark model, run inside your browser, looks at the photo and returns hundreds of points on the face: the outline of the jaw, the eyes, the nose, the lips and the forehead. The tool uses the MediaPipe Face Landmarker. Your photo is not sent to ToolStack Hub; only the model files are downloaded the first time you use it.
Step 2: take four measurements
| Measurement | What it is |
|---|---|
| Face length | From the top of the forehead to the chin |
| Cheekbone width | The widest part across the cheeks, used as the reference |
| Jaw width | Across the corners of the jaw |
| Forehead width | Across the upper forehead |
Step 3: compare ratios
Every measurement is divided by the cheekbone width, so the size of the photo does not matter. The tool then applies simple rules, tested in this order:
- Face length of at least 1.38 times the cheekbone width: oblong.
- Jaw at least 0.90 and forehead at least 0.85 of the cheekbone width: square (or oblong if the face is also long).
- Forehead more than 0.10 wider than the jaw: heart.
- Forehead and jaw both under 0.85 of the cheekbone width: diamond.
- Length under 1.22: round.
- Anything else: oval.
For example, a forehead of 13.6, cheekbones of 14.0 and a jaw of 10.6 (in cm) give ratios of 0.97 and 0.76. The forehead is much wider than the jaw, so the estimate is heart.
How reliable is it?
Treat the result as a starting point, not a verdict. The cut-off values are simple rules that we have not validated against a set of labelled faces, and many faces sit between two shapes. Several things also move the numbers:
- Head tilt or turn. The tool warns when the face looks turned.
- Hair over the forehead, which changes where the top of the face seems to be.
- Expression and lens distance. A close phone camera widens the centre of the face.
- Lighting and shadows that hide the jaw line.
Taking a good photo
- Use even daylight and hold the camera at eye level at arm’s length.
- Pull hair back from the forehead and face the camera with a relaxed expression.
- Use one face per photo. If several faces are found, only the first is used.
No photo? Measure by hand
The manual option accepts the same four measurements in any unit, as long as all four use the same unit. Use a soft tape measure and keep the tape flat against the face.
What face shape does and does not tell you
Face shape describes proportions only. It says nothing about health, identity or attractiveness, and the styling ideas that go with each shape are common suggestions, not rules. Choose glasses and haircuts you like.
Frequently asked questions
Does the detector store my photo? No. The analysis happens in your browser.
Why does my result change between photos? Small changes in angle, light and expression shift the ratios, and a face near a boundary can land in different shapes.