People have long tried to come up with other potential indicators to determine the size of a guy’s manhood without actually seeing it. A seemingly tried and true method for doing just this is to look at the size of the man’s hands and/or feet. But does hand and foot size really correlate to the length of the penis?
Nope.
Studies have consistently shown that the size of a guy’s feet or the overall size of their hands is not related to their member’s erect measurement. However, a man’s fingers do give a strong clue as to their probable penis size- but the overall length of the fingers is not what’s important here.
For instance, a study published in the Asian Journal of Andrology in 2011 found that the ratio between the 2nd and 4th digits on the hands strongly correlates with the overall length of an individual’s penis.
The lower the ratio- how much shorter the index finger is than the ring finger- the longer the penis will probably be when erect. (And if you’re wondering, flaccid penis length is not an accurate predictor of erect penis length.) More specifically, you can calculate your ratio by taking the length of your index finger (measured from the crease where it meets your hand, to the tip) and divide it by the length of your ring finger. The shorter your index finger is compared to the ring finger, the lower the ratio will be and, if you’re a man, the longer your penis probably is.
The 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.
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.
Here comes the technical part
So why does the ratio of the index and ring finger lengths correlate to erect penis length? In the beginning, female and male genitals are pretty much the same. This is because they develop from the same cluster of tissues (gonads). In males, somewhere around weeks 7-9 of gestation, the gonads begin secreting two hormones- Anti-müllerian hormone (AMH) and testosterone. AMH prevents the development of the ducts that eventually turn into the fallopian tubes, the uterus, and upper vagina.
Once the gonads begin secreting testosterone, some if it (around 5-10%) gets transformed into another hormone called dihydrotestosterone. Both testosterone and dihydrotestosterone will attach to androgen receptors, which affect the growth and development of many different body systems.
So to sum up here, penile growth in the womb is stimulated and affected by testosterone, dihydrotestosterone, and androgen receptors. Circulating amounts of the two hormones, combined with the associated androgen receptor stimulation, will determine penis size.
So what about fingers? Circulating testosterone in the womb will affect other body parts as well- pertinent to the topic at hand, including the ratio between the 2nd and 4th digits (index and ring fingers).
Why does testosterone affect digits differently? essentially the activity mediated by androgen receptors, and estrogen receptor-a, is higher in your ring finger compared to your index finger. This is regulated by the structure of genes controlling the process for the bone growth of your fingers, called endochondral ossification. The spread of chondrocytes will determine the length of your finger, and this expansion is higher in the ring finger compared to the index finger.
When you decrease the activation of androgen receptors during the narrow window of digit development (usually completed by week 13 of gestation), you will decrease the length of your ring finger. This activation is attributed to amount of testosterone and DHT circulating throughout the tiny fetus. Conversely, if you decrease the activity of the receptor estrogen-a (the ones being stimulated more when you’re female), you will get a longer ring finger.
Based on this physiology, it has been long known that you can predict prenatal hormone exposure based on the ratio of these two fingers. Since both penile length and the ratio of the ring and index finger is basically a result of the amount of testosterone and DHT circulating in utero, there is a correlation between that ratio and the length of a man’s favorite appendage.
As you might have guessed from all this, the ratio between the lengths of one’s index and ring fingers is usually quite different in men and women- men tend to have shorter index fingers than ring fingers; women tend to have their index fingers either the same length or longer than their ring fingers.