The "Fifty Shades of Grey" erotic trilogy, which has garnered lots of attention and criticism, is expected to hit the 20 million-sales mark in the United States this week, said The Wall Street Journal on Monday.
Pop culture blog Vulture put it a different way: the trilogy has accounted for one in every five hard-copy fiction books sold this past spring.
"It's entered the cultural conversation, which has made the trilogy much bigger than books often are," said Anne Messitte, the publisher of Vintage Books, an imprint of Random House which released the books in the US, according to The Journal.
The Journal said that between its March publication and July 2, the trilogy had already sold 19.4 million copies in print and e-book format, according to Nielsen BookScan. The Stieg Larsson trilogy, starting with "The Girl With the Dragon Tattoo" took three years to reach that mark, after its release between 2008 and 2010.
The trilogy has sold 31 million copies worldwide in English-language markets and the movie rights were acquired by Universal Pictures and Focus Features, said The Journal.
More on GlobalPost: 'Fifty Shades of Grey' trilogy sales hit 10 million
Critics have been scathing about the writing style of the books which feature a college student named Anastasia Steele who falls in love with a tall, dark and handsome stranger who's into bondage, according to The Los Angeles Times. The books have been labeled "mommy porn" for their readership base consisting mainly of 30-something women. The story's origins as "Twilight" fanfiction are no big secret.
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E.L. James' agent said, "This did start as 'Twilight' fan fiction, inspired by Stephenie Meyer’s wonderful series of books. Originally it was written as fan fiction, then Erika [E.L. James] decided to take it down after there were some comments about the racy nature of the material. She took it down and thought, I’d always wanted to write. I’ve got a couple unpublished novels here. I will rewrite this thing, and create these iconic characters, Christian and Anna. If you read the books, they are nothing like 'Twilight' now," according to The LA Times.
Speaking on a British TV show in April, James said, "I am completely stunned by the reaction to these books. Generally I’m getting emails that say, 'really loved the book, and my husband thanks you too’," according to The Daily Telegraph.