Penis size linked to finger length: Study

By Dr. Ananya Mandal, MDJul 7 2011

A new South Korean study shows that the ratio of the length of a man's index finger to that of his ring finger is linked with penis size. The lower the ratio the longer the penis, say researchers. The study was published in the Asian Journal of Andrology.

The researchers looked at 144 Korean men who were hospitalized for urological surgery. A researcher measured the patients' penile length — flaccid and stretched — just after they went under anesthesia for their operations. A different researcher measured the men's finger lengths, in order to prevent knowledge of one measurement unconsciously affecting the other.

Results showed that those with a lower ratio, whose index finger (or second finger, 2D) was shorter than the ring finger (or fourth finger, 4D), had a longer stretched penis length, which is well correlated with erect size. Lead researcher Dr. Tae Beom Kim of Gachon University in Incheon, Korea writes, “Based on this evidence, we suggest that digit ratio can predict adult penile size.” The other researchers involved in the study are In Ho Choi, Khae Hawn Kim, Han Jung, Sang JinYoon, and Tae Beom Kim, of Gachon University Gil Hospital (Incheon, South Korea), and Soo Woong Kim, of Seoul National University College of Medicine (Seoul, South Korea).

Previous studies have linked the so-called 2D:4D ratio of finger length with exposure to the sex hormones estrogen and testosterone in the womb. So it's possible that the same exposure may affect penis length. Higher testosterone levels during fetal development are associated with a lower 2D:4D ratio, while higher estrogen levels are connected with a higher one. Most men have index fingers that are shorter (low ratio) than their ring fingers, while most women's index fingers are the same size or longer (high ratio) than their ring fingers. Research has shown, however, that lesbians and female-to-male transgendered people are more likely to have more “male” ratios.

Of course, it remains to be seen whether the correlation between penis size and 2D:4D ratio holds true in non-Korean men or in Korean men who aren't having some type of urological surgery. An easy and non-invasive measurement, it could give doctors a quick way to gauge how much testosterone their patients were exposed to in the womb, wrote Dr. Denise Brooks McQuade of Skidmore College in Saratoga Springs, N.Y., in an editorial accompanying the study.