Measurement guide

Gonial angle

The angle at the back corner of the lower jaw, between the rear edge of the jaw (the ramus) and its lower border. A smaller angle makes a squarer jaw corner, a larger one a more sloped corner.

How it's measured

Clinically it's measured on X-rays: one line along the back edge of the ramus, one along the lower border of the jaw, and the angle where they meet at gonion, the jaw corner.

From a side photo you measure the same corner on the skin outline instead: a point on the back edge of the jaw below the ear lobe, the jaw corner, and the jawline running forward. Muscle and soft tissue sit over the bone, so a photo gives an estimate of the bony angle rather than the same number.

Typical values

X-ray studies of adults commonly report averages of about 120° to 125°. In one study of 98 adults, the mean was about 123° with a standard deviation of about 7° (Bhullar et al., 2014). Some studies find slightly larger angles in women than in men on average (for example Abuhijleh et al., 2019); others find almost no difference (Bhullar et al., 2014).

What changes the number in a photo

• Not a true profile. If the head is turned toward the camera, the jaw corner is foreshortened. Shoot a true side view, with only one eye visible.
• Chin tucked. Tucking the chin bunches the skin under the jaw and blurs its lower border. Keep the head level.
• Hair and collars. The back edge of the jaw below the ear has to be visible. Tie long hair back and clear the neck.

One number, one feature

The gonial angle describes one corner of the jaw. Jaw width, chin position and the neck line shape a profile just as much.