How Big Is Enough? Women Confirm This Flaccid Length Is the Sweet Spot — Plus 2 Other Functions Beyond Reproduction

People often say “size doesn’t matter, technique does.” But a study published in the scientific journal PLOS Biology offers a different perspective. Australian researchers found that while size does influence attractiveness, men tend to care about it far more than women do — and often seriously overestimate how important it is to women.

A research team from the University of Western Australia invited more than 200 women and 600 men to rate computer-generated images of men. These images varied in height, shoulder-to-hip ratio (the classic V-shaped torso), and genital size.

The results showed that women did find taller men with a V-shaped physique and larger genitals more attractive. Specifically, when the penis in its flaccid (non-erect) state was longer than 4 inches (about 10.3 cm), women rated it as attractive.

However, lead author Dr. Upama Aich pointed out a key difference: women’s preference shows a “diminishing returns” effect. Once size exceeds a certain point, further increases do not make the man more attractive — interest levels off or even declines.

Men’s Perspective: Bigger Is Always Better

In contrast to women’s more measured view, men showed no such diminishing-returns pattern. Male participants generally saw larger penis size as a sign of greater sexual competitiveness and physical threat among other men.

Dr. Aich analyzed: “Men consistently viewed same-sex individuals with exaggerated traits (such as very large size) as more sexually threatening. This suggests men often overestimate how important these traits are for attracting women.”

More Than Just Reproduction

Why do humans have this perception gap? Co-author Professor Michael Jennions explained from an evolutionary biology angle that the human penis is relatively large compared to body size among primates — something that has long puzzled biologists.

He noted: “Although the primary function of the penis is to deliver sperm, the findings suggest that its unusually large size evolved as a kind of ‘sexual ornament.’” Before clothing became common, it was a visible trait used both to attract women and as a status signal to deter rivals.

Age Also Plays a Role

Interestingly, the study found that the observer’s own characteristics influenced the ratings. Taller women placed more importance on men’s height. And as men got older, they paid more attention to the penis size of potential rivals when evaluating them. Researchers speculated this could stem from heightened awareness of sexual competition or accumulated experience about women’s preferences.