Penis length cannot be determined by how big his hands or feet are -- those and other supposed indicators have been widely discredited for years. But now a team of Korean researchers has produced what may be a more reliable guide: the ratio of the length of his index finger to that of his ring finger. The lower that ratio, the longer the penis may be, the researchers wrote Monday in the Asian Journal of Andrology.

Dr. Tae Beom Kim, a urologist at Gachon University in Incheon, Korea, and his colleagues studied 144 men over the age of 20 who were undergoing urological surgery for conditions that do not affect the length of the penis. One member of the team carefully measured the lengths of the index and ring fingers on the subject’s right hand before surgery -- left hands are thought to be more variable. A second team member then measured penis length immediately after the subject had been anesthetized. The length was measured both when the penis was flaccid and when it had been stretched as much as possible. Stretched length is thought to correlate to erect length, the team wrote. The team found that, in general, the lower the ratio of the lengths of the two fingers, the longer the stretched length of the penis.

Although it may seem like the results are coming out of left field, they actually are not. A variety of studies suggest that the ratio of the two finger lengths is determined by prenatal exposure to sex hormones, both testosterone and estrogen. It is not unreasonable to assume that penis length might also be.

Men and women are what is termed sexually dysmorphic in terms of finger lengths. In women, the index and ring fingers are generally the same length, while in men the index finger is generally shorter. Researchers from UC Berkeley created a stir in 2000 when they reported that lesbian women tended to have a ratio of the two finger lengths that was more typical of men. But the situation was more complicated for men. The team found no difference in the ratio between gay and straight men unless they had several older brothers -- a factor which had previously been linked to being homosexual. Such men were found to have an unusually low ratio of the finger lengths.


Other recent research has suggested that men with a lower ratio have a more symmetrical face and are more attractive to women, a phenomenon known as the “sexy ratio.” And just last year, researchers from Warwick University and the Institute of Cancer Research in Britain reported that a man’s risk of developing prostate cancer is related to the ratio of the two digits. Men whose index finger in longer than their ring finger were found to be one-third less likely to develop prostate cancer.

Digit ratios are noninvasive and easy to measure and thus may provide a surrogate for studying prenatal development in men, wrote Dr. Denise Brooks McQuade of Skidmore College in Saratoga Springs, N.Y. in an editorial accompanying the study.