When people shop on the virtual shelves of Amazon, Barnes & Noble, Apple, or Kobo, chances are that they are looking for books within a specific category. Categories constitute one the most important metadata elements for every book, and using the appropriate categories is critical for discoverability of e-books in online stores.

Because major online booksellers handle e-book categories in different ways, you need to bear three critical facts in mind:

1. The number of categories you can use varies from bookseller to bookseller.

2. There is no standard list; categories can vary between stores.

3. Using as many categories as you can is essential.

Categories allow shoppers to drill down within ever finer classifications of a topic to books they want to buy. For example, a top-level category such as ARCHITECTURE can have dozens of subcategories, from Adaptive Reuse & Renovation, to Buildings, to Urban & Land Use Planning. Several of these subcategories may have sub-subcategories; for example: ARCHITECTURE / Buildings / Landmarks & Monuments.

Even though this description is three levels deep, it will be defined by online booksellers as a single category.

Besides helping shoppers find e-books they will want to buy, choosing the right categories may help your book get bestseller standing, A book in a highly competitive category may never reach the list of top 10 or 25 bestsellers, but put it in a less competitive category and it might stand a chance.

Of course, I am not advocating that you assign unrelated categories to a title, because doing so could create one of two potential problems. First, your targeted readers may never find the book. And second, people who buy it may be disappointed and angry about being misled, with the result that the book gets bad reviews and/or buyers return it for a refund.

Category limits vary not only by store but by aggregator. The chart below shows the number of categories four major online booksellers allow you to select, and the number allowed by two of the more mainstream aggregators specializing in distributing e-books to e-bookstores.

Note that even though all the stores allow you to select multiple categories, using these aggregators limits your selection. Smashwords sets the limit at two, and Bookbaby sets it at one, which means that the category you select in Bookbaby will be the only category it lists for every store it serves, even though the stores all allow more than one.

Smart Category Choices

Using the BISAC Subject Headings available at bisg.org as a starting point  (bisg.org/what-we-do-0-136-bisac-subject-headings-list-major-subjects.php), select at least five categories that apply to every e-book you want to sell, always remembering that a category can be as deep as three layers. Again, don’t stretch the truth about the book’s content. Keep the categories relevant. And see “Using BISAC Subject Headings” via Independent Articles at ibpa-online.org for additional guidance.

A key point: The category lists for particular stores and aggregators often differ from the BISAC Subject Headings list. Be prepared to select the closest match to your original selections when a bookseller doesn’t offer an exact match.

Then look up your competition in each selected category at each bookseller’s site and note the number of books, plus the pub dates, the average ratings, and so on for each competing title. Think about each category you’ve chosen in terms of whether it is one that might give your book a shot at category bestseller status. Then prioritize your selected categories according to relevance and opportunity.

That way, when you provide categories for a book to each store, or to an e-book distributor, the book will have a stronger chance at getting found. And the better the chances of its being found, the better the chances of its being bought, which will mean higher sales rankings, maybe even category bestseller status.

David Wogahn is the author of Successful eBook Publishing and managing partner of the e-book services and digital media consulting company SellBox.com. To learn more: david@sellbox.com or Linkedin.com/in/wogahn.