So how does the regular man size up? The mean length of a flaccid penis is 3.6 inches, and the mean length of an erection is 5.16 inches, according to a paper titled "Am I Normal?" published Tuesday in the British Journal of Urology.
To ascertain such delicately precise numbers, British researchers assessed the merits of 96 previous papers dealing with male private parts, excluding most because they focused on health issues like erectile dysfunction. For this meta analysis, that left 20 valid studies, each conducted to gauge a dude's height and circumference down there. The total members in this unique scientific gathering: 15,521.
The project's goal, said lead author Dr. David Veale, was to construct "nomograms" — graphical representations — of penis measurements spanning all ages and races.
More from NBC News:
Dentists doing dermatology? Cosmetics lure docs of all types
'Far-reaching' storm to bring snow, chill to millions
Where Netanyahu's speech has already succeeded—and where it has failed
"The nomogram provides reassurance about what a normal size of a penis is," said Veale, a consultant psychiatrist at the South London and Maudsley NHS Trust.
For many women, the only size that matters "is usually the girth," Veale wrote in an email. "This is because the most sensitive part of the vagina is in the outer regions."
In the paper, Veale and colleague add: "Men may present to urologists or sexual medicine clinics with a concern with their penis size, despite their size falling within a normal range. This type of concern is commonly known as 'small penis anxiety' or 'small penis syndrome.' "
Read MoreSex sells: 50 shades of green
The "definitive" nomograms may help clinicians counsel these men, the authors wrote. The measurements also may help "investigate the relationship between condom failure and penile dimensions."
The authors concludes that past research has shown 85 percent of women were satisfied with their partner's penis size, but only 55 percent of the men were satisfied with their own size.
In reality, raw numbers don't mean much when it comes to pleasing a partner, said an expert who read the paper.