Amazon Sales Rank, Secret Algorithm Exposed
Amazon Sales Rank, how do they figure it? A lot of Indie authors want to know exactly what to expect with sales rank when they sell ebooks on Amazon. For instance, how many ebook sales does it take to reach the 10,000 mark, or the 1,000 mark or *gasp* the top 100 best sellers? Like Fermat's Last Theorem and Google's algorithm for determining search results (minus about 200 factors), Amazon Sales Rank algorithm seems to be a highly guarded secret.
It's human nature to want to understand things. Unfortunately, Amazon won't give us an X + Y + Z = Sales Rank equation. They have said, "As an added service for customers, authors, publishers, artists, labels, and studios, we show how items in our catalog are selling. The lower the number, the higher the sales for that particular item. The calculation is based on Amazon.com sales and is updated each hour to reflect recent and historical sales of every item sold on Amazon.com."
The first question that comes to mind is how many ebooks does Amazon sell? There are plenty of ebooks with no sales ever, therefore no sales ranking, which makes it difficult to know how many are really out there. 5 million ebooks? 7 million? 10 million? Since books have shown up in the 4 million range with at least one sale, it's safe to assume this number is reaching 10 million.
Just my opinions but what seems to be true (and these are estimated numbers based on Amazon US Kindle ebooks);
a book must have a sale (even just one) to be ranked.
it only takes a few sales to leap from the millions to the hundred thousands, as in going from a ranking of 4,156,977 to 357,954 after just 3 sales.
it only takes about a dozen monthly sales to break the 100,000 mark.
then to break the 10,000 mark, the 1,000 mark and the top 100 mark – the sales have to multiply in geometric progression (a heck of a lot).
to be in the top 100 best selling books, (estimating here) sales must routinely be well over 200 sales/day.
from the above info, an important factor appears to be how many recent sales have occurred.
Okay, this can't be rocket science. Sales happen over time. Factors are pretty limited: total number of sales ever (history) and recent number of sales (the past month, week, day, hour). Since Amazon updates rankings hourly, it can be deduced that Amazon factors at least 2 major numbers into the equation: the total number of sales ever, history, and the total number of sales hourly. In my experience of watching the numbers move up and down, there have been many hours of the day where some of my books didn't sell any copies and the ranking only changed slightly, so it also seems logical that daily sales and weekly or even monthly sales must also play into this equation. In fact, it's logical that all of these factors play a role, perhaps some more than other and perhaps from hourly to daily to weekly to monthly in importance. That's got to be it or close to it; what else could possibly go into the equation?
Here's a telling comparison. The #1 best selling book from 2009 (New Moon, Book 2 of Twilight Series by Stephanie Meyer) shows a current Amazon sales rank of #936. Another book that was published just 4 months ago in May 2011 (The Mill River Recluse by Darcie Chan) is currently ranked #2 on Amazon. Yet another book published last month in August 2011 (Thunder Dog by Michael Hingson) is ranked #4. There is no way the latter books have anywhere near the total number of sales as New Moon. This would seem to indicate that hourly sales are far more important to the equation than total sales ever (history). Apparently Amazon places a huge priority on ranking what is hot right now and certainly makes recent sales the number one factor. In fact, 4 of the top 10 bestsellers were published this year while the oldest book in the top 10 is from 2002, another is from 2007 and the rest from 2009 or more recent. Ah-hah, time is by far the number one ingredient. (This is great news for Indie authors; get your sales rolling and you could make the top of the charts in little time as there is much evidence that exposure from the top of the charts boosts sales dramatically.)
Something like this below could be the secret equation to determine sales ranking or how one book compares to all other Amazon books:
hourly (# of sales) x daily/2 x weekly/3 x monthly/4 x history/10 or more = Sales Corresponding Coefficient (SCC)
This way the main ingredient is time, namely hourly and daily, with slightly less emphasis on weekly and even less on monthly and last on history. The SCC of any book with substantial sales can be a huge number; the highest number would have the lowest sales ranking. It should also be noted than a zero (0) for any of these categories other than history should not make the formula reduce itself to zero. Perhaps every other category besides history should have a 1 added to the equation to force a real number to be the outcome.
What happens to books with the exact same number of SCC? Whichever book has been on the shelf longer would rank lower.
What about price affecting ranking? This has been mentioned but seems seriously doubtful. Evidence does suggest that lowering the book's price can lead to more sales and free books get downloaded like crazy, but it's hard to imagine Amazon would want to encourage the cheaper books to have a better ranking as they would make less money that way. Could the opposite be true, could higher priced books get better ranking? Perhaps but doubtful again, since the top 10 bestsellers currently have 4 books priced at 99 cents.
This theory is just my opinion; Amazon sales ranking places priority over recentness of sales by hour, day, week and month while also factoring in a small percentage for total sales history. It's a a fun thing to conjecture upon but probably not too helpful in selling ebooks. If you want to read more on the subject by some pretty focused people who have spent far more history on this, a Google search or these links might be useful – http://ebmv.blogspot.com/ and http://futureperfectpublishing.com/2008/01/27/dark-mysteries-of-the-amazon-sales-rank/.
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