'Fifty Shades' biggest hit since 'Harry Potter'

(CNN) - Last year, author E.L. James was sitting in her living room looking for ways to make some cash. Now, the author of the trilogy "Fifty Shades of Grey" is raking in the dough and breaking some serious records. It is the biggest book juggernaut since "Harry Potter."

The erotic trilogy, which tells the story of a 27-year-old billionaire and a college student, is smashing records quicker than you can turn a page.

In the UK and its overseas territories, the trilogy has sold more than 4 million copies in traditional and e-books combined. In the U.S. and Canada, it sold 15 million copies in the first three months it went on sale. Reports now put sales close to the 20 million mark.

The tantalizing page-turning plot may entice women, but electronic readers have helped the more conservative reader sample the book unnoticed, and that has started a trend.

To feed demand, mainstream publishers are launching digital-only erotic labels. HarperCollins in the UK recently launched Mischief Books with the tagline "private pleasures with a hand-held device."

E-readers are also fueling a different type of surge - self-publishing. "Fifty Shades of Grey" became a best-seller without starting off with a traditional publisher. Now others are doing the same.