Purpose Despite multiple studies regarding modes of eyebrow measurement and movement over time, the lateral aspect of the brow has been relatively ignored in literature. Therefore, we arranged a study of the most lateral aspect of the eyebrow; in doing so, we hoped to ascertain the most practical line or angle of measurement. Methods In this cross-sectional study, adults aged 18 and older with no history of congenital or acquired periorbital or orbital pathology or surgery; brow tattooing or heavy plucking; phthisis; or strabismus were measured using a combination of in-office metrics and computer analysis. Subjects were asked to identify their ethnicity and country of origin. Models of age, gender, age and ethnicity were created. Results 1024 subjects were included (1944 eyes). Measurements of nasal ala to lateral brow (NALB), lateral brow plumb line (LBPL, the vertical line between the tail of the brow and a horizontal line extending from the lateral canthus), and angle from the mid-brow to the lateral brow tail all showed statistically significant decline over time. The angle and LBPL varied most by ethnicity. The angle narrowed approximately 3 degrees per 20 years, while the LBPL fell approximately 2.5 mm per 20 years. The NALB varied most by age, and fell approximately 3 mm per 20 years. Conclusions The lateral tail of the brow descends with age. Measurements of its location and rate of change vary between genders and within ethnic groups. Two easily measured values – NALB and LBPL – can be used for pre-operative planning and post-operative documentation.