The average American man's penis is 5.6 inches long when erected. Penis size has been the subject of dozens of studies, as well as countless urban legends, myths and spam emails. For many men, the idea of not measuring up can cause a great deal of anxiety.
But whether penis size truly matters to a man's sex partner is up for debate. Some research shows that women who experience vaginal orgasms do so more consistently with men of bigger penises. Other work suggests bigger isn't always better: One study found that ideal penis size depends on a person's height, and another showed that girth matters more than length to most women.