Some Book Bub numbers and petunias

My attention was drawn to a set of numbers from BookBub available here: https://www.bookbub.com/partners/pricing?fbclid=IwAR1mMlf6nO5oAS5QN0pD-9V-NRAxkdNz6AQMNOJurGT1NnD_DQEjiPzOEL0

Some major caveats before we go into them. Firstly these are for marketing purposes and as they say “averages are based on historical data, but are only meant as a reference and are not guaranteed”. The book figures also only apply to free downloads and discounted book sales. Lastly, these are BookBubs numbers and other retailers of books may show different patterns.

A broader caveat to add when considering any kind of average sales within books (or other media) is the dreaded power-law distribution. A small number of books account for a large number of sales and conversely a large number of books account have small sales individually but account for a lot of sales together. The arithmetic mean has many flaws but it is particularly flawed in such circumstances. One huge hit (e.g. The Da Vinci Code) will have an outsized impact on the average book sales even if other books are selling poorly.

Tables and things after the fold…

The relevant figures provided (with variable symbols I’ve picked):

  • BookBub subscribers by genre category [P]
  • Free book average downloads [D]
  • Discounted book average sold [S]

You can use these categories to compare the relative popularity of genres. For example Crime Fiction & Thrillers have the most BookBub subscribers but Cozy Mysteries & Crime Fiction have the most free downloads whereas Crime Fiction & Historical Fiction have the most sales.

Now, if you are genre shopping as an author, can you use this data to pick a sweet spot for selling books? For example, if Crime Fiction and Historical Fiction both sell well then maybe Historical Crime Fiction is the best genre? True Historical Mysteries do sell well but as they are a more narrow genre they sell less well then Crime or Historical fiction in general but there is a trade off there. A narrower genre definition must have smaller numbers but every book is a subgenre of 1. Broad genres sell more but they are also more crowded with books.

Last week our old chum Dave Freer posted about these numbers at Mad Genius Club (https://madgeniusclub.com/2020/02/17/super-readers-and-their-interests/). He was very interested in defining a sweet spot:

“Of course if the interest in that category is small, the download/sales numbers are small. Of particular interest is what translates into paid sales. The areas to look at warily are those where a lot of people will download for free, but few buy. The ideal ‘sweet spot’ is reasonable volume (high interest) reasonable percentage of free downloads, and high paid percentage. A high paid percentage may seem desirable but if that’s off low interest number, and low ‘exploratory’ (free download) percentage, that’s not too good for new authors, but possibly OK for established ones.”

That strikes me as an odd combination of factors. Given the numbers there is a simpler question that can be asked: which genre has the best chance of a book selling? I’ll come back to that.

Dave decides on a index that is calculated as:

“A QUICK ‘DIRTY’ CALCULATION OF NEWBIE SWEET SPOT ( a lot of interest – a lot of experimenting with new to them authors -free, and a high percentage of sales) RANKED (NUMBER INTERESTED*FREE PERCENTAGE*PAID PERCENTAGE)”

Using the variables I named earlier that is P*(D/P)*(S/P) or D*S/P. Consider for a moment what on Earth that might be calculating. It is simply arithmetic nonsense. In units it is downloads-squared divided by people. There’s no rhyme or reason to multiplying the free downloads by the paid-for downloads. I assume he thought he was finding a fraction of a fraction but it really doesn’t work out that way.

A rationale for this odd choice becomes clearer when Dave lists the top 16 fiction (maybe) sub-genres. By his index the LGBT and African American Interest end up at the bottom of his list.


A sweet spot is easier to find within the limitation of the numbers we are given. Firstly we can put the subscribers number [P] aside. That number will largely be determined by how we define categories (broad categories have a bigger P). We want to make an estimate of how well a book might sell (it will be flawed and probably not a very good estimate). We don’t need the P number because we have actual sales. We do want to factor in how crowded the subgenre might be and we can work that out using Free Downloads plus Sales [D+S]. We can add these numbers because they are the same kind of things (i.e. essentially the same units).

Sales divided by total downloads (free and paid) gives a meaningful (up to a point) index [S/(D+S)]. It is the proportion of sales compared to the total number of downloads. That gives you Table 1 below. LGBT as a category does very well. Why? Because even though it is a small category, more of the books in the category SELL. Christian Fiction does not do well here because it’s proportionally a lot more free downloads.

If you want to throw the subscriber number in you can but what you end up with is what I’d call bookshop categories (Table 2). Literary fiction tops the list because it is a very broad category and it has proportionally a lot of sales. Table 2 is very unremarkable.

CategoryS/(D+S)
Politics and Current Events20.00%
LGBT15.53%
Religion and Spirituality10.77%
True Crime10.51%
Business10.45%
Middle Grade10.38%
Literary Fiction10.25%
Christian Nonfiction9.86%
Science9.84%
Historical Fiction9.84%
Historical Romance9.22%
African American Interest9.09%
Biographies and Memoirs8.51%
General Nonfiction7.68%
Cooking7.22%
Paranormal Romance7.15%
Supernatural Suspense7.15%
History6.91%
Dark Romance & Erotica6.89%
Humor6.84%
Time Travel Romance6.62%
Psychological Thrillers6.59%
Science Fiction6.48%
Women’s Fiction6.37%
Advice and How-To6.34%
Romantic Suspense6.27%
Children’s6.19%
Christian Fiction6.02%
Thrillers5.93%
Crime Fiction5.79%
Erotic Romance5.73%
American Historical Romance5.69%
New Adult Romance5.56%
Fantasy5.46%
Chick Lit5.44%
Contemporary Romance5.33%
Action and Adventure5.08%
Historical Mysteries5.05%
Teen and Young Adult4.88%
Horror4.45%
Cozy Mysteries4.11%
Parenting2.70%
Table 1: S/(D+S)
CategoryP*S/(D+S)
Literary Fiction323,760
Historical Fiction305,993
Biographies and Memoirs280,738
Crime Fiction267,414
Thrillers210,000
Psychological Thrillers198,462
General Nonfiction189,631
Historical Romance166,942
Historical Mysteries154,026
Women’s Fiction145,965
History142,447
Contemporary Romance138,012
Science Fiction132,848
Religion and Spirituality132,462
Action and Adventure131,578
Cooking119,924
True Crime115,639
Cozy Mysteries115,559
Supernatural Suspense115,052
Fantasy113,565
Romantic Suspense113,524
Christian Nonfiction101,599
Politics and Current Events98,000
Advice and How-To93,263
Humor82,051
Paranormal Romance81,522
Teen and Young Adult81,009
New Adult Romance74,489
Business72,090
Erotic Romance69,849
American Historical Romance68,842
Science65,952
Middle Grade64,340
Chick Lit62,607
LGBT55,913
Christian Fiction51,784
Horror50,781
Dark Romance & Erotica45,451
African American Interest41,818
Children’s40,838
Time Travel Romance39,054
Parenting14,054
Table 2

23 thoughts on “Some Book Bub numbers and petunias

  1. I love love that this is tagged Straw Puppy.

    “There are three kinds of lies: lies, damned lies, and strawtistics.”
    -Bortsworth Chronicle and Daily Commercial Advertiser

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  2. He ignores the rather obvious that some mystical ‘sweet spot’ does nothing for you if you are selling what the buyer does not want. There are fewer Black and LGBT sales than Christian, but what if I want a Christian romance with black or LGBT main characters? In fact, that is where figuring Bookbub gets complicated. (I have over the years run some twenty promotions, by the way, so I’ve run into a few complications)

    For instance, one of the subgenres I write is medieval historical mysteries. Now you’d think they should go in historical mysteries, but most buyers in historical mysteries are not looking for medieval ones. It tends toward Regency and Victorian. (A pity, but it is what it is). My mysteries do best in the much larger and according to him ‘not sweet spot’ historical fiction category. My two points being 1. Avoid his blog and 2. know your market and what isn’t your market.

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    1. I didn’t know that about historical mysteries — I just assumed it would be medieval.

      Victorian I’d think of as regular mysteries because there are contemporary mystery stories from that time (ie it’s not a genre mash up to mix Victorian times with detectives)

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      1. Historical mysteries extend well into the 20th century by now. Currently, fluffy 1920s set historical cozy mysteries featuring crime-solving flappers are particularly popular, probably as a result of the Miss Fisher Murder Mysteries series. And I’ve recently seen a historical mystery series set in the 1950s, featuring yet another crime solving socialite.

        Also, a lot of historical mysteries these days seem to be cozies, e.g. the above mentioned crime solving socialites and flappers. That’s not really an audience that will be particularly interested in J.R.’s gritty medieval mysteries.

        As for avoiding that blog and particularly that author, Cam has been chronicling the follies going on over there for a while now.

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      2. I wouldn’t call them historical mysteries any more than I would call Jane Austen historical romance. These authors were writing contemporary stories for a contemporary audience, even if their books are dated now.

        What I was referring to are new mysteries set in the 1920s written by authors who live in the 21st century. And those are undoubtedly historical mysteries.

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      3. IDK if you have heard of Volker Kutscher whose books were made into “Babylon Berlin” (stupid title imho) but they’re another good example. The first book was published in 2008 or so but it spans from the Weimar Golden Twenties. They’re hardboiled/noir historical crime fiction.

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      4. A question – if new mysteries set in the 20’S are historical mysteries, but works from that vintage aren’t, what is the status of fanfic of Dorothy Sayers and Agatha Christie?

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  3. As soon as I saw that the post was by Dave Freer, I braced myself for some serious bad math and indeed, there it was. Statistics and Dave are not friends.

    And while it’s only anecdotal evidence, I can confirm that LGBT fiction sells very well indeed, because it’s a small but hungry market. My second bestselling title of all time is a lesbian sweet Christmas romance short story.

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  4. “Sales divided by total downloads (free and paid) gives a meaningful (up to a point) index [S/(D+S)].”

    I’m not sure I agree that’s meaningful – or at least, I don’t think it gives the kind of number Freer seem to want.

    AFAICT Freer’s goal is to find a genre where a) many curious readers will try out a new author, and b) many serious readers will pay for books they like.

    The simplest way to express that is to simply add S+D. Or perhaps better, [D + ( S * m)] – where m is some kind of multiplier to express that paying readers are much more interesting than curious freeloaders. But I don’t think it’s right to divide by total downloads – a genre with D=100K and S=10K is not better than one with D=200K and S=10K

    A major point, however, is that (at least if I understand this correctly) Book Bub’s numbers for “Sold” is for discounted books, not full price. I’m sceptical to using that number to measure how willing the readers of a given genre is to pay for books they like. To get a good measure of the purchasing power of readers in different genres, we need full price numbers.

    (Yes, I’m procrastinating.)

    Liked by 1 person

    1. //But I don’t think it’s right to divide by total downloads – a genre with D=100K and S=10K is not better than one with D=200K and S=10K //

      The thing is consider a category like “books” or “fiction”. If the category is sufficiently broad then the values for D & S will be large but not in a helpful way. However, as you point out more interest is best expressed with straight sales figures but I think only if you felt two categories were actually comparable. Of course, an actual author picking genres isn’t going to be deciding between Erotica and Christian genres but will have a small number of genres in mind. In that case just treating the three values separately and making a judgement call is probably best.

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      1. “If the category is sufficiently broad then the values for D & S will be large but not in a helpful way. ”
        But the numbers are average sales and downloads pr book, aren’t they? How broad the category is doesn’t matter for that. A small genre with 1000 books and a broader one with 5000 books will have comparable averages.

        Liked by 1 person

      2. Very true BUT bigger categories really do have bigger D+S because the distributions are wacky. A bigger category will have a bestseller that is bigger (or more likely to) or more of them. Big sellers have a disproportionate impact on the averages pushing up the means more than is intuitive. See my caveat about power law

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      3. If you plot the subscriber value P against the total (D+S) you can see visually what I mean. Fit a line of best fit and it has a r-squared of 74%. Mean Number of sales+downloads really is proportional to subscribers and substantially so.

        But…maybe something is revealed in the discrepancies…

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      4. “If you plot […] ”

        Hmm, that sounds too much like work and not procrastination. I think I’ll take your word for it. I thought a broad genre will also have more low-selling titles to average out the bigger best-sellers, but I guess I’m wrong about that.

        But does that mean subscriber number really is an indication of popularity and not just broadness? I realize that we lack another number that would have been useful: The number of titles in each category. [ P / titles ] would have been a useful way to measure genre popularity.

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      5. //The number of titles in each category. [ P / titles ] would have been a useful way to measure genre popularity.//

        Yes, that would be handy or a median number of books bought per subscriber or the modal number of books bought by a subscriber. These would be much more useful for making a decision with.

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  5. So he basically juggled a bunch of made up numbers so he could say that LGBTQA+ and African American Interest (whatever the hey that is,) don’t sell? Broad categories and sub-categories in terms of popularity are already widely known. If he wants a “sweet spot,” he can just look it up.

    Non-fiction sells better than fiction and is the back-bone of the book publishing market. Non-fiction also gets media coverage, t.v. and radio interviews for promotion, merchandising and seminar tie-ins, etc. making it possible to build very profitable multi-pronged platform brands for non-fiction books, as opposed to fiction. In non-fiction, authors directly compete and marketing and advertising strategies actually work, unlike fiction. If you want to be financially successful as an author, you don’t write fiction. You leverage your expertise as an information provider for non-fiction. If you don’t have any particular expertise, you become a journalist/researcher on a subject to provide the info, team up with someone who is an expert on a subject, or in the case of things like self-help, make up a philosophy you sell as expertise.

    In non-fiction, business/finance has long ruled the roost since businesses will do block buys of titles on management, etc. and since people look for basic financial advice. The books there have very quick turnovers because the information ages very quickly, but they are the reliable sellers. Second is self-help, including health and diet books. While there are varying trends in self-help that move in and out in popularity, self-help/self-improvement stuff always sells. Political stuff is wildly unpredictable but has been a financially useful category for publishers. What they used to call “serious” non-fiction — history, science, sociology/culture — is a less popular grouping but has been very reliable and has a much longer shelf life than business or self-help, plus can cross-over sales to the educational and university markets.

    If you must do fiction and you want the “sweet” genres, you’d usually do mystery/suspense, especially if you are a white man. Suspense and romance are basically tied for most popular categories of fiction, with one doing better than the other some years (depending on how you deal with romantic suspense,) and romance having a paperback advantage. Suspense is certainly the higher status category with more media coverage. The most popular sub-category of suspense are “thrillers.” But that’s a very broad label — it gets put on nearly everything that has heavy action and/or a dark tone where there are high stakes. You have both standalones and mystery series in thrillers and there’s been lots of debate about which strategies are more likely to be successful but it’s pretty much a wash. Series have longevity and staying power. Standalones that hit well in sales are more likely to be adapted for film/t.v.

    Romance and romantic fiction have been a major force in fiction since the mid-20th century. They used to make up 50% of the paperback sales until the wholesale market collapse in the 1990’s but still do make up about a third of the paperback sales. They also have the longest running and most successful electronic publishing market, are regularly adapted for t.v. films and own land in every other book category that you can dream up, including extensively in SFF. A decent percentage of romance writers are men, as are readers, but the market is seen as predominantly women and it’s an easier entry field for many women writers, plus you can be super prolific in it without that being a problem for publishers or self-publishing fans.

    Science fiction and fantasy together form a dual category market that is basically third, about twenty percent of the market, not counting YA or SFF romance and only counting horror titles published in the category SFF market. When you add in all the horror fiction published in the general fiction market, 90% of which is SFF, then they are solidly third. And right now, SFF hits have a nice chance at film/t.v/game adaptation.

    YA/juvenile/New Adult is a separate market from the rest of retail trade fiction. It has had growth from the late 1990’s onward, including in non-fiction. YA fiction continues to be a fruitful market for authors, all areas. Historical fiction is not the sweet spot if you want to be a big seller with lots of bestselling titles, but it is a really large sub-category of general fiction and sells really steadily for a lot of authors. Contemporary drama/fiction also does really well and has a good rate of adaptation for its bestsellers. But they aren’t as attractive to authors who are looking to sell to trends.

    Religious fiction, which is mainly Christian fiction in the English language market, is a separate industry from retail trade fiction and is part instead of the Christian publishing market, which is mainly non-fiction. Christian fiction expanded considerably from the 1970’s into the 1990’s, went through a stagnation period where Christian publishers consolidated and went out of business, but in more recent times sells very well. If that’s your jam, it can be quite successful. However, it’s a smaller number of publishers and can be harder to break in.

    If a fiction author really wants to maximize sales possibilities, writing as many different books in as many different genres as you can has been an effective strategy. The big example of this is James Patterson, who first became a bestselling mystery thriller writer with his Alex Cross series (he’s white but Cross is a black character,) but then set out to write romances, contemporary fiction, YA, science fiction, etc. in many different genres, on the belief that the more he could do books in various genres, the wider an audience he would have, (he came from advertising). Then he started teaming up with other writers to do this faster. And then he went whole hog into being a book packager selling to his regular publisher as a partnered imprint. He comes up with or approves outlines that his hired collaborators then write for him (they get name credit, a cut and a boost for their own solo fiction.) Hiring a stable of writers has also become popular with some in the self-publishing area of the market. Some of these book packaging arrangements can be predatory, and some book packaging arrangements are not as broad, targeting particular sub-genres rather than a wide base. But if you’re looking for a sweet spot, spreading yourself out across fields, with or without help, can be effective and then you don’t have to worry about which sub-category is doing better than others at a given time.

    In Australia, where I seem to remember Freer lurks, romance, fantasy and crime/suspense are the ones that have had expansions in recent years, along with YA/juvenile, though Australian authors usually have to sell outward to the global English language market.

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