There doesn’t seem to be a direct way to answer this.   Book sales data appears to be kept very private between authors and publishers, probably for the same reason that you never tell anyone your income.  In any case, books are a highly durable product and can last for centuries, so knowing modern sales figures wouldn’t say much about how many books were sold long ago.

But maybe we can answer this a different way.  The website LibraryThing lets you keep a catalog of your own library online.  It currently has 2.2M members, and 122M works cataloged, representing 11.7M unique titles.  I use it myself.   It can show the number of works held by its members by author.   This can tell us how popular authors are, at least among these bibliophilic and technophilic users.   They’re far from a random sample of readers, but they’re probably more similar to you, if you’re reading this blog post.

The most popular author by this standard is J. K. Rowling, who has 625,782 works in the collection as of this writing.  That’s 0.5% of all the books listed!   For other authors, let’s express their popularity as a percentage of hers, rather than by somewhat meaningless raw copy counts.   The webpages also show which individual book has the most copies, so let’s also look at whether that book dominates the author’s total.  It even shows the total number of works held, although that can include a lot of really minor stuff.

I sampled a lot of authors in this spreadsheet: LibraryThing Author Statistics.  Many of them write in multiple genres, but I assigned them to the genre of their biggest book. I did make an exception for Ursula K. Le Guin, because I’m a fan.   Below is how it looks for the top 20 SF authors.  Click on the link to see the author’s full list on LibraryThing:

Author	Lived	% of Rowling copies	Book with Most Copies	% of author’s total	# works
Isaac Asimov	1920 –1992	29.6%	Foundation	7.6%	1901
Orson Scott Card	1951–	23.8%	Ender’s Game	20.8%	340
Anne McCaffrey	1926 –2011	23.7%	Dragonflight	4.1%	262
Kurt Vonnegut	1922 –2007	22.2%	Slaughter house-Five	23.7%	227
George Orwell	1903 –1950	21.4%	1984	43.3%	266
Douglas Adams	1952 –2001	21.4%	The Hitchhiker’s Guide to the Galaxy	20.9%	110
Robert A. Heinlein	1907 –1988	20.2%	Starship Troopers	7.1%	341
Margaret Atwood	1939–	19.0%	The Handmaid’s Tale	22.7%	187
Ray Bradbury	1920 –2012	16.2%	Fahrenheit 451	35.6%	803
Ursula K. Le Guin	1929 –2018	14.9%	A Wizard of Earthsea	10.8%	397
Philip K. Dick	1928 –1982	14.7%	Do Androids Dream of Electric Sheep?	14.1%	525
Frank Herbert	1920 –1986	13.4%	Dune	31.0%	178
Arthur C. Clarke	1917 –2008	13.4%	2001: A Space Odyssey	10.7%	482
Neal Stephenson	1959–	13.0%	Snow Crash	18.5%	70
Larry Niven	1938–	11.0%	Ringworld	10.1%	299
Aldous Huxley	1894 –1963	10.6%	Brave New World	59.1%	234
William Gibson	1948–	10.6%	Neuromancer	25.8%	51
Iain M. Banks	1954 –2013	10.2%	Consider Phlebas	7.8%	54
H. G. Wells	1866 –1946	9.8%	The Time Machine	19.7%	898

Asimov wins! And he’s not just known for Foundation. And there are an enormous number of works under his name, 1901, which is unsurprising given that he wrote over 500 full books.  The authors with the most works are him, Wells, Bradbury, Dick, and Le Guin, who all had long, productive careers.

Orson Scott Card and Ann McCaffrey come in at #2 and #3, which higher than I would have expected.  Likewise Heinlein at #6 and Clarke at #12 are lower.  I’m pleased that Iain M. Banks made it onto the list, and if you added in his non-SF work (published as just Iain Banks), that would add another 3%.

Orwell, Bradbury and Huxley are mainly known for one work, but those works are major.  McCaffrey, Heinlein, and Asimov had the lowest percentages for their biggest book, showing what diverse output they had.

There are only a few living authors (although we just lost Le Guin!), and only three women, so this represents an older view of the field.  This might well be an older audience, one that has had time to build up enough of a library to want to catalog.

For comparison, let’s look at the top 10 genre authors:

Author	Lived	% of Rowling copies	Book with Most Copies	% of author’s total	# works
J. K. Rowling	1965–	100.0%	Harry Potter and the Philosopher’s Stone	14.9%	177
Stephen King	1947–	77.6%	The Gunslinger	3.3%	664
Terry Pratchett	1948 –2015	61.1%	Good Omens	6.3%	312
J. R. R. Tolkien	1892 –1973	48.3%	The Hobbit	21.5%	620
C. S. Lewis	1898 –1963	46.1%	The Lion, the Witch and the Wardrobe	10.1%	618
Neil Gaiman	1960–	45.9%	American Gods	9.1%	575
Stephenie Meyer	1973–	28.2%	Twilight	26.1%	72
Dan Brown	1964–	23.8%	The Da Vinci Code	38.3%	35
Dean Koontz	1945–	22.7%	Odd Thomas	4.2%	342
Mercedes Lackey	1950–	21.3%	Arrows of the Queen	2.3%	295
George R. R. Martin	1948–	21.0%	A Game of Thrones	21.4%	494

Fantasy sells a lot more than SF!  Six authors here are bigger than Asimov, including the youngster Neil Gaiman.  The youngest author in both these lists is Stephenie Meyer, followed by Rowling.

Are you dismayed that fantasy and SF seem to dominate people’s collections?   Don’t worry – classic authors do very well too:

Author	Lived	% of Rowling copies	Book with Most Copies	% of author’s total	# works
William Shakespeare	1564 –1616	40.8%	The Complete Works of William Shakespeare	9.0%	4336
Agatha Christie	1890 –1976	36.8%	And Then There Were None	5.2%	1502
Jane Austen	1775 –1817	30.6%	Pride and Prejudice	29.8%	705
Charles Dickens	1812 –1870	29.3%	Great Expectations	14.2%	1841
Mark Twain	1835 –1910	19.2%	Adventures of Huckleberry Finn	24.2%	2040
Ernest Hemingway	1899 –1961	17.4%	The Old Man and The Sea	19.3%	501
Fyodor Dostoevsky	1821 –1881	16.6%	Crime and Punishment	29.8%	952
Gabriel Garcia Marquez	1927 –2014	15.0%	One Hundred Years of Solitude	35.1%	289
Arthur Conan Doyle	1859 –1930	14.4%	The Hound of the Baskervilles	10.0%	2350
F. Scott Fitzgerald	1896 –1940	14.1%	The Great Gatsby	58.0%	425

Big Bill is way up there, and blows away those lightweights with 4336 works.  Even the foreign language authors Dostoevsky and Marquez rate highly in terms of number of copies.

Is this a fair measure overall?  It’s certainly not a measure of overall influence – Austen and Dickens are clearly more important authors than Rowling or King.   It’s probably not a good measure of actual unit sales either, but that only matters to investors in publishing houses.  Maybe it’s best thought of as a sense of what people who care about books have actually read.    You’ve probably heard of all of these authors.   If not, give them a try!