Evolutionary anthropologist Helen Fisher agrees, and adds length isn't the only measure that matters.
"When women tell you that size doesn't matter, they're either lying to you or they're lying to themselves. Or they haven't had very much experience. It's one of those three. Because size does matter," Fisher said.
And a woman we spoke with agreed. "Length is a biggie but you gotta have the girth with it, it's the combo really. Got to have it all," she said.
And that's why there's a billion-dollar penile-enlargement industry, selling pills, potions and other products that all say they can make a man larger. But experts say there's no evidence any of these products work.
So it seems men -- and the women they love -- must live with what nature provided them.
Loreen Stevens is livin' the single life. She calls New York City "candyland."
"It's like eye candy everywhere you look. Guys are giving you cards, they're giving you lines," she said.
Shows like "Sex and the City" help perpetuate the conventional wisdom that young and single means lots of fun and lots of good sex, but the 34-year-old Stevens says that's not what she's found.
"I don't want to say it's lonely, but it's so unfulfilling. I'm not comfortable with the casual nature of sex in this city," she said.
J.J. Kandel, another single in the city, has decided that casual sex just isn't satisfying any more.
"It's about finding the right person," said the 24-year-old actor.
Both Kandel and Stevens have stopped prowling and instead are focusing on their careers.
"Emotionally, it's very expensive to put yourself out there and give yourself to people, so let it happen as it will. If I am 70 years old when I find my husband, then so be it," Stevens said.
The movie "Old School" perfectly captures our belief that marriage kills your sex life. Vince Vaughn's character mocks one of his recently married buddies for deciding to have sex with only one person for the rest of his life.
But the real joke is that marriage actually makes sex better.
A University of Chicago study shows that married couples are having more sex -- an average of six times a month, vs. four times a month for singles of the same age. And it's not just more sex, it's better sex.
"Ultimately it's intimate sex that's the most satisfying and fulfilling because the other person already accepts you. They'll accept cellulite or they'll accept potbellies," said clinical psychologist Ellen McGrath.
McGrath says couples who take time to nurture their relationship outside the bedroom will have a better sex life. "They think it's about sex. It's not about sex. It's about the quality of the connection outside the bedroom," she said.
Mark and Dawna Nocera are award-winning professional dancers who teach at their studio in Woburn, Mass. After 15 years of marriage, they say their sex life has never been hotter. They say a great marriage and great sex is very much like a dance. McGrath thinks they've found the secret to great sex and a great marriage.
"Somebody who's just starting out dancing doesn't know anything about the experience that you have 20 years later when you really move," said Mark Nocera. "I think sex is very much like that. It takes a lot of rehearsal to make dancing look that easy."
Porn is a man's domain and a turnoff for women, right?