Today’s Wonder of the Day was inspired by Amy from McLean, IL. Amy Wonders, “What is the most popular book of all time?” Thanks for WONDERing with us, Amy!

Do you love to read? If so, you've come to the right place! Wonderopolis is filled with all sorts of Wonders of the Day to read. Just look around. You're sure to find many Wonders of the Day that will arouse your curiosity.

Of course, if you love to read, there's nothing better than a good book. Like a best friend, a good book is always there for you, just waiting to help you grow and learn. As you open a favorite book, you're instantly transported into a story that, for at least a little while, becomes a whole new world to inhabit and explore.

For those who love books, it's natural to WONDER about what the most popular book of all time might be. Like many such questions, though, there's not an easy answer that everyone can agree upon.

For example, how do you measure the popularity of a book? Is the most popular book of all time the one that has been read the most often or the one that has sold the most copies? No matter which guide you use, though, there are problems making precise calculations.

How can you know how often a book has been read? Should it count if the same person has read the book more than once? Sales figures would seem like an easier way to measure popularity. Unfortunately, accurate and precise sales figures aren't available for many older books, some of which are amongst the most popular of all time.

Also, what about libraries? Many people check out books from their local library rather than buying copies to keep at home. Some people check out and read a favorite book over and over again. How would you account for these instances in terms of calculating popularity?

As you can see, determining a book's popularity isn't exactly straightforward. However, there are a couple of books that most experts agree are probably two of the most popular books of all time: the Bible and the Koran. The holy texts of Christianity and Islam, respectively, these books have been printed billions of times.

Guinness World Records estimates that over five billion copies of the Bible have been sold, making it the best-selling book of all time. Because religious texts are often translated into many foreign languages and distributed widely by churches, however, precise figures are hard to come by. For this reason, such religious texts are often excluded from lists of the most popular books of all time.

Likewise, accurate sales figures are hard to come by for popular books that happen to be very old, such as Don Quixote, A Tale of Two Cities, The Three Musketeers, Les Misérables, Pride and Prejudice, and the Odyssey. Despite these difficulties, reliable and independent sources have been used to estimate some amazing sales figures for several well-known books.

As examples, Don Quixote has been estimated to have sales of 500 million copies and A Tale of Two Cities, the Charles Dickens classic, has estimated sales of over 200 million copies. Other best-selling books with sales of over 100 million copies include: J.R.R. Tolkien's The Lord of the Rings and The Hobbit, Antoine de Saint-Exupéry's Le Petit Prince (The Little Prince), and J.K. Rowling's Harry Potter and the Sorcerer's Stone. If you add up the sales totals for all the books in the series, Rowling's Harry Potter series has sold over 450 million copies!

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