The allure of the Amazon.com sales rank is well known to many an author, as is the bewilderment it often brings. How convenient—a number that tells you in hard, empirical terms how your book is doing! But alas, the Amazon sales rank is a fickle mistress. After noticing wild fluctuations in their placement, authors and publishers often fall prey to obsessive rank-checking, waking up at night in cold sweats to boot up the computer and surf to Amazon.com, spending endless hours staring bleary-eyed at the monitor: Refresh, refresh, refresh, refresh, refresh.

Yet for all this scrutiny, the Amazon sales rank remains cloaked in mystery. Derived from a complex algorithm that the folks at Amazon are not about to give out, the rankings take into account more than just how many copies of a certain title have been sold. There are varying decay rates, predictive curves, tiers with different refresh rates, historical analysis. Rather than regurgitate the inconclusive findings of studies that try to identify Amazon’s secret formula by buying books and painstakingly analyzing the changes in rankings, let’s first identify what we know for sure about the system.

• The smaller the rank number, the more books you’re selling. Perhaps this is obvious, but to clarify—the number one spot is reserved for the top seller. As your relative sales go down, your rank number goes up.
• Not all books are updated hourly. And in fact, some books are updated more frequently than that, as the seasoned refresh button junkie will tell you. It all depends on the range you fall in. Books between 1 and 10,000 are re-ranked at least hourly. Books between 10,000 and 100,000 are re-ranked once a day. Those beyond 100,000 are re-ranked weekly.
• After you sell one book, you get a rank. There is one slot per book, so no two books have the same ranking. As your book sells more, it moves up the ladder; as other books outsell yours, it moves back down.
• Total historical sales are part of the equation, but not a huge one. For instance, Martha Stewart’s latest book has no problem towering hundreds of slots over, say, Catcher in the Rye at the moment. This is because her book has sold more copies at a faster rate within a recent time span, not because she’s sold more copies overall.

The most important thing to remember about your sales rank is its temporary and relative nature. The Amazon rating is more like a popularity contest than the litmus test for a book’s success. The number you see on the page is merely how you’re selling compared to other titles in a very brief period. Two or three purchases of the same book within an hour can send a title skyrocketing up the rankings. Sure it’s exciting to leave a few thousand of your competitors in the dust, but unless the buying continues at a good pace, you can slip from the higher rankings fairly quickly.

By the same token, don’t feel sick if following your rankings feels like riding a particularly nasty roller coaster. For a more accurate assessment, get an average ranking: check the rank once an hour for twenty-four hours if you’re in the top 10,000, once a day for a week or two if you’re between 10,000 and 100,000, once a week for a couple of months if you’re lower than that. This will give you a much more stable picture of how your book is selling online. Services like titlez.com can show you a graph of a particular book’s historical rankings. Titlez.com is in beta testing and currently does not list all titles, but you can request that a particular book be added. At booksandwriters.com, you can register to receive email reports on your rankings for a small fee.

Remember also to take seasons into account when assessing your sales rank. Students buying for the upcoming semester can clog the top spots with textbooks and paperback classics in the late summer and midwinter seasons. Likewise, books without gift appeal will probably see a significant drop in the holiday months.

But in the end, the sales rank is meant to be, in Amazon.com’s words, merely “interesting.” Don’t sweat it if you can’t figure out why your number is exactly where it is. Instead, focus your energy on making your product page as informative and consumer-friendly as possible. It has been our experience in optimizing Amazon pages that the product’s rank improves as it collects additional content. Whether good reviews and number of hits have a direct effect on the sales rank formula is unclear; it’s more likely that books with more detailed pages simply attract more buyers. Either way, ensure that your product page does a good job of representing your product.

For those of you interested in deducing sales numbers from rank and trying to crack the magical algorithm, read Morris Rosenthal’s What Amazon Sales Ranks Mean or this report from MIT’s ebusiness center. If you don’t have the time for übercomplicated mathematical gymnastics, just remember that your ranking depends on many variables we’ll probably never fully identify. Enjoy the spikes in your number—you’re selling copies fast—but don’t forget that the Amazon.com sales rank does not make the book.