In the new study, researchers at Gachon University Gil Hospital in South Korea recruited 144 volunteers 20 years of age and older who were going to undergo urological surgery. While the men were under anesthesia, the researchers measured their finger lengths and both their flaccid and stretched penis lengths. Stretched penis length is statistically correlated to the size of the penis when fully erect.
The average flaccid penis length, the researchers found, was 3.0 inches (7.7 centimeters), with a range of 1.6 to 4.7 in. (4 to 12 cm). Stretched lengths ranged from nearly 3.0 to 6.7 in. (7.5 to 17 cm), with an average of 4.6 in. (11.7 cm).
The average ratio between the two fingers was 0.97, with a range of 0.88 to 1.12, making the differences hard to make out with the unaided eye. But the lower the digit ratio, the study found, the longer the penis was likely to be.