Rule of Fifths: Analyzing Facial Width
- Nerve
- Highlighted area
Quick facts
- Definition
- Division of the face width, in frontal view, into five vertical parts of similar width.
- Reference measure
- The width of one eye, from the inner corner to the outer corner.
- Central fifth
- Distance between the inner corners of the eyes, which tends to be close to the width of the nasal base.
- Complements
- The division into thirds, which assesses facial height.
- Relevance in orofacial harmonization (HOF)
- Helps read the width of the cheekbone, nose, mouth and jaw, with ethnic and individual limits.
The rule of fifths is a model for analyzing face width: in frontal view, the face is divided into five vertical parts, each about the width of one eye. The central fifth runs from the inner corner of one eye to the other, the next two cover the eyes, and the two outer ones run from the outer corner of the eye to the lateral limit of the face, at ear level. It complements the division into thirds, which assesses height.
What do the five fifths look like?
| Fifth | Limits | What is usually compared |
|---|---|---|
| Central | Inner corner of one eye to the inner corner of the other | Width of the nasal base, which in the classic model is similar |
| Two medial lateral | Inner corner to outer corner of each eye | Width of each eye and symmetry between them |
| Two outer | Outer corner of the eye to the lateral limit of the face | Projection of the cheekbone and temple, and jaw width |
Other relationships are often read together: mouth width at rest is compared with the distance between the inner edges of the irises, and the width between the jaw angles with the width between the cheekbones. These are observation references, not target measurements.
Why does the rule of fifths matter in orofacial harmonization (HOF)?
- Cheekbone and temple: the outer fifths show whether lateral width is deficient, balanced or dominant, which guides the conversation about the cheekbone and temples.
- Nose: a nasal base wider than the central fifth is a common finding and cannot be corrected with filler. Knowing this avoids a wrong indication.
- Jawline: the width between the angles influences the reading of a square, oval or narrow face, a topic covered in square face: assessment.
- Asymmetry: comparing the fifths on both sides, starting from the facial midline, helps document facial asymmetry before any procedure.
What are the limits of the rule?
The rule of fifths comes from the neoclassical canons used in art. Anthropometric surveys show that many faces seen as harmonious depart from these proportions, and the patterns change with ethnic origin, sex and age. That is why it serves to organize observation and explain the reasoning to the patient, not to define a target face. The same applies to the golden ratio.
How does it show up in the assessment?
- Standardized frontal photo: camera at eye level, at a fixed distance, face without rotation. A slight tilt already distorts the outer fifths. See standardized clinical photography.
- Neutral expression: a smile widens the mouth and changes the cheeks.
- Documentation: noting the findings in the patient record with the photo helps comparison after treatment.
Also called: facial fifths, rule of five eyes, horizontal proportion of the face.
Frequently asked questions
How do you apply the rule of fifths to a face?
On the standardized frontal photo, draw vertical lines at the inner and outer corners of the eyes and at the lateral limits of the face, at ear level. The classic model expects five similar bands, each the width of one eye, and the differences are a point for observation, not automatic correction.
Does the rule of fifths apply to everyone?
Not as a rigid rule. It is a reference model derived from classical artistic canons, and facial measurement studies show that many people considered harmonious do not follow the exact proportions. Ethnicity, sex and age change the patterns.