Inspired by the Author Earnings report, I’ve taken a quick whack at looking at what percentage of Kindle ebook sales self-publishers represent by genre. To get there, I simply look at the top 100 bestsellers in each genre—romance, mystery/thriller/suspense, science fiction, and fantasy—and split them up by method of publication. Note that, unlike the Author Earnings study, this is merely a breakdown of the raw number of self-published titles on the bestseller lists, not the number of total book sales within each genre.

Also, instead of five categories of publisher, I use four: self-published, small/medium press, Amazon Publishing, and Big 5 (including, where appropriate, major genre publishers like Harlequin and Baen). For books where the publishing method was unclear, I did a search of the house. If the house published only a single author’s works, I listed it as self-published. If the house published multiple authors, even if it was obviously an author collective, I listed it as small/medium.

Okay! Without further ado, the numbers:

ROMANCE

Self-published: 49%
Small/medium: 11%
Amazon: 9%
Big 5/Harlequin: 30%

MYSTERY/THRILLER/SUSPENSE

Self-published: 11%
Small/medium: 5%
Amazon: 16%
Big 5: 68%

SCIENCE FICTION

Self-published: 56%
Small/medium: 9%
Amazon: 5%
Big 5 (plus Baen): 30%

FANTASY
Self-published: 49%
Small/medium: 7%
Amazon: 7%
Big 5: 37%

One of these things is not like the other! At an immediate glance, one thing is clear: if you’re publishing in romance or SF/F, self-publishing is an extremely viable method. Roughly half of all the bestselling books in each of these genre is self-published. That’s pretty remarkable.

For mysteries and thrillers, however, it’s a different story. Of course you don’t have to be a bestseller to make a living as an independent author, but it’s equally remarkable that just 11% of the top 100 mysteries and thrillers are self-published. That suggests two things. If you’re a thriller author, you may want to keep querying agents. Or that there’s a market inefficiency in thrillers, where there aren’t enough good indie titles to meet demand. It’s also possible that both of those things are true! I couldn’t say.

Also, it should be said that this is just a look at the top 100 in each genre out of hundreds of thousands of total books. It’s quite possible, perhaps even likely, that a broader look at the data would present different trends. However, it does match up well with the Author Earnings study of these genres combined, so I’m not sure a bigger sample would be that much different.

Of course, there’s one more big factor here: each genre’s total share of the Kindle market. Fortunately, that’s really easy to ballpark. By looking at the #100th-ranked book in each genre and dividing that by its overall Kindle rank, we get an estimate of what percentage of the entire Kindle market each genre represents. For instance, if the #100 book in Romance were #1000 in the Kindle store, we could figure that 1 in 10 sales, or 10%, are of romance books.

Here’s how it shakes out:

Romance: 40%
Mysteries/Thrillers: 20%
Fantasy: 6.33%
Sci-Fi: 5%

You’ll note that adds up to 71.33%. Hugh Howey’s much bigger and better sample suggested these four genres comprise 69% of total Kindle sales (though it didn’t break it down by genre). To me, this means the above numbers should be pretty accurate, despite the crude methodology used to determine them.

Obviously, romance is the runaway winner. There is a huge market for it and self-publishers do very well there. Fantasy and science fiction are about neck and neck: fantasy is a little bigger, market-wise, but self-publishers have more share of the science fiction market. Mysteries and thrillers have a very big overall market—half as much as romance, and a fifth of all Kindle sales—but taking advantage of the size of that market appears to be a challenge for self-publishers.

Also, if the Author Earnings report didn’t already make this perfectly clear—holy shit self-publishers sell a lot of books. I knew we’d taken over a big part of the market. I didn’t know that, within three of the four most popular genres, we’d taken half of it.

Quick edit: I should make it perfectly clear that these percentages are very preliminary. Where the Author Earnings report samples nearly 7000 books, including about 2600 of the top 7000 titles in the Kindle store, I’m only sampling the top 100 in each genre. In a sample that modest, even a small variance from the norm might throw things out of balance. For instance, if just five of the books in fantasy were switched from self-published to Big 5, the numbers of each would be nearly equal. I will try to remember to run this again in another month or so and then again later in the year to see whether the results hold.

That said—there are several signposts the data’s pretty accurate. For one thing, among three genres, the percentages are pretty similar across the board. For another, although I divide things up differently, and am only measuring number of titles instead of number of sales, my results are pretty close to those of the Author Earnings survey—which was taken, to my knowledge, 2-3 weeks ago. The lists I looked at today were certainly comprised of many different titles, yet the number of self-published titles on both studies is pretty close. This makes it less likely that either study is an anomaly.

Ultimately, though, time will tell.