Women are more attracted to men who are well endowed, scientists in Australia have said.
The research team from the Australian National University found that women prefer tall men who have broad shoulders, narrow hips and a large penis.
Brian Mautz and Michael Jennions showed 105 women over 50 life-size computer generated male figures with differing heights, body shapes and penis sizes.
To create the computer generated images, the team used the measurements of over 3,300 young Italian men. The images ranged in body shape, height and penis size - between five centimetres (1.9 inches) and 13cm (5.1 inches).
Women were then asked to rate how attractive the male images were.
The researchers found that the most attractive penis size was larger than that of 95 percent of men - in excess of 13 centimetres in their flaccid state.
They found the figures women found most attractive were tall men with large penises: "We've found that penis size did influence a man's sex appeal, and it was just as important as height, which is a well-known factor in male attractiveness," Jennions said.
Mautz added: "To put it bluntly, if you are short and pear-shaped, a large penis is not going to increase your attractiveness."
There was also no upper limit to how big penis size could get to be attractive: "Our curve wasn't going down at 13 centimetres so we did not reach the most attractiveness in terms of size.
"The concept of a penis that was 'too big' was outside the range that we tested and we simply didn't find an absolute maximum size, even though it strikes me that it is going to start to look ridiculous and actually quite painful.''
On average, women judged the figure's attractiveness in three seconds, and were even faster when viewing the less attractive figures.
"Now that's quick," Mautz said. "That's so quick that you can't really, in that short space of time, consciously go through the pros and cons of each character; that rating is an overall impression of attractiveness, not focused on any particular body part."
Jennions said their study is important to human evolution as it suggests women prefer better endowed men: "Humans have slightly longer, and notably thicker penises for their body size compared to other primates.
"It's been suggested that, before humans wore clothes, females used penis size as one of the deciding factors when choosing a mate, but until now there has been very little data to support that.
"Our results hint that humans might have larger penises because females in the past were more likely to mate with well-endowed males."