Penis Size: It May Be Written in the Length of His Fingers

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Photo-Illustration by Alexander Ho for TIME; Getty Images

The ratio of the length of a man’s index finger to that of his ring finger may seem like a strange thing to measure, but new research suggests that it’s linked with penis size. The lower the ratio, the longer the penis.

The new study was conducted on 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.

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They data suggested 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.

“Based on this evidence, we suggest that digit ratio can predict adult penile size,” the researchers, led by Dr. Tae Beom Kim of Gachon University in Incheon, Korea, wrote.

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 plausible 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.

Finger-length ratios have been linked previously with a variety of other characteristics: in both males and females, lower ratios are associated with better athletic performance. In men, one study found that a lower ratio was connected with more success at high-frequency financial trading, while another study associated it with better performance on medical school entrance exams; women were not included in those studies.

Men with lower 2D:4D ratios were also more likely to have more “masculine” features, to have more symmetrical faces, and to be considered attractive by women, according to another study.

Yet other research links low 2D:4D ratios with higher rates of alcohol consumption and alcoholism itself. Some data suggest that a more “female” finger-length ratio in men is associated with increased risk for oral cancer but reduced risk for prostate cancer.

In both boys and girls, lower and more “male” 2D:4D ratios have also been repeatedly connected with autism; interestingly, a recent study also found that female-to-male transgendered people are more likely to have autistic traits.

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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.

But if so, digit ratio could be good for more than just a pick-up line at a bar. 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.

The study was published in the Asian Journal of Andrology.

Maia Szalavitz is a health writer at Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.