Bigonial width ratio

The jaw corners sit at the sides of the lower face, where the outline begins to turn towards the chin. When they are nearly as wide as the cheekbones, the sides of the face look straighter. Corners that sit farther inward make the outline narrow below the cheeks, which can make the cheekbones appear more prominent.

This comparison also explains why a broad jaw does not always look broad relative to the face. Someone with especially wide cheekbones can have substantial jaw width and still receive a low ratio. In a narrower face, a smaller jaw may nearly match cheekbone width and produce a higher result.

Jaw-corner width establishes the sides of the lower face, while chin width determines how it finishes. Broad corners leading to a broad chin retain width across the region. With a short lower face, this can look square; with more height, the same widths can form a longer, rectangular outline.

Broad corners can also lead to a narrow chin. The jaw remains wide at the sides but turns inward towards a finer point, so a high bigonial ratio can occur in a tapered lower face. When the corners and chin are both narrow, that taper begins higher, just below the cheeks. Additional height then makes the lower face look more slender and elongated.

A relatively broad chin beneath narrow jaw corners creates less narrowing near the bottom. Its rounded or flatter lower edge becomes more noticeable because the sides above it are already close together.

Narrow temples and a narrow jaw make the cheekbones stand out between them, creating a diamond-like outline. Broader temples above the same jaw give the face a more gradual taper from top to bottom. The jaw can therefore contribute to different overall shapes without changing its own width.

Below the jaw, a narrower neck leaves a visible inward step under the corners. A neck close to jaw width reduces that separation and makes the outline more continuous. This is why a wide jaw may look less defined than a narrower one sitting above a much narrower neck.

The lower face grows substantially on the way to adulthood. Its width develops alongside its height, and larger adult faces can also differ in shape. In the celebrity sample studied by Salinas, Liu and Sharaf, men had longer and wider lower faces, while women showed more taper towards the chin. The difference involved the whole lower outline rather than jaw width alone.

The visible corners include the masseter muscles and the soft tissue covering the bone. Clenching may make the sides fuller, while other tissue changes can round the contour. A broad span with rounded edges can consequently look quite different from the same span with a sharply turning jawline. Compare relaxed photographs when assessing a change in width or definition.

The 0.75–0.85 reference describes jaw corners that retain substantial width while remaining narrower than the cheeks.

The experiment "Perceptions of female jaw angles, intergonial widths and gonial heights" found a preference for narrower jaw-to-cheek relationships in its female stimuli. Mogilski and Welling also found that jaw prominence affected ratings when varied with other features. These findings concern the faces and alternatives tested; they do not establish the reference interval as a preferred width for every chin shape or lower-face height.