According to research which was commissioned by the Publishers Association and Frontier Economics, book to movie adaptations gross 44% more at the U.K. box office and 53% more worldwide than films from original screenplays.
Other interesting finds include:
43% of the top 20 highest-grossing films in the U.K. from 2007 to 2016 were based on books.
9% were based on comic books.
Movies based on books not only boost sales of ticket holders but also in turn tend to boost sales of the books which the movies are based on.
An example of this is the HULU 2017 television adaptation of Margaret Atwood’s The Handmaid’s Tale which boosted sales of the dystopian novel in the same year.
In August 2017, Netflix acquired indie comic book publisher Millarworld who can now publish it’s books in tandem with their Netflix adaptations.
Books to film/TV is showing no sign of slowing down with several adaptations just this year including:
12 Strong by Doug Stanton
Maze Runner: The Death Cure based on The Death Cure by James Dashner
Peter Rabbit based on The Tale of Peter Rabbit by Beatrix Potter
Fifty Shades Freed by E L James
Red Sparrow by Jason Matthews
Love, Simon based on Simon vs. the Homo Sapiens Agenda by Becky Albertalli
A Wrinkle in Time by Madeleine L’Engle
Crazy Rich Asians by Kevin Kwan
Boy Erased by Garrard Conley
How the Grinch Stole Christmas! by Dr. Seuss
The Guernsey Literary and Potato Peel Pie Society by Annie Barrows and Mary Ann Shaffer
Although The Publishers Association report does not have an exact answer for why movies adapted from books gross much higher than original screenplays or why more people watch TV shows based on books or comic books, my professional opinion is that a book has the unique advantage of creating a “built-in audience” turning all those “readers” into “ticket buyers” who will certainly bring along at least one or two more people with them to watch the movie.