Penis length has grown 24%, on average, in 29 years, Stanford study finds
The average length of an erect penis has grown 24% over the past 29 years, according to a new medical study, even as other research has shown that sperm count and testosterone levels are falling.
Penile length might not be directly related to fertility, said Dr. Michael Eisenberg, a urologist and male fertility specialist at Stanford Medicine who led the research, published in The World’s Journal of Men’s Health.
But anything that changes the reproductive system is fundamental to human existence and “something we should pay attention to and try to understand,” Eisenberg said.
Given declining sperm counts and testosterone levels, he thought he would find that penis length was shrinking as those levels fall and as men, in general, get more obese.
“It certainly was very surprising,” he said of his findings.
Studies have measured penile length dating back at least 80 years, according to Eisenberg, whose team compiled data from 75 studies conducted between 1942 and 2021 on nearly 56,000 men around the world.
The increase they found was apparent in different regions of the world. “This was not isolated to a specific population,” Eisenberg said.
The average length of the erect penis across all regions and decades was about 5.5 inches, the study found.
Dr. James Hotaling, a University of Utah Health urologist and men’s infertility specialist, praised the study but said he’s not convinced that penises today are longer. The simplest explanation, he said, would be that the method of measurement has changed, though there’s no evidence that has happened.
Hotaling said it’s unclear what the clinical impact of this finding might be, but he agreed it contradicted his expectations: “This would not support the sperm apocalypse.”
Eisenberg thinks the change in length might be explained by earlier puberty. Boys, like girls, have been reaching puberty earlier in recent years. Perhaps, he said, that’s giving their bodies a longer time to grow overall.