Wouldn’t it be great to look at an Amazon sales ranking for any book and know how many it sold? You’d be able to forecast selling your book on Amazon, help select the categories your book should be in, and know how much your competitors are making.
Selling Ebooks On Amazon
I mean, how many books do you sell with an Amazon sales ranking of 50,000? Or 5,000? Or 500?
One thing is for sure–Amazon isn’t going to tell you. A well-designed correlation study is the only way to find out. So I kept track of the sales ranking and units sold for six of my ebooks over a 90-day period in 2012. I then commissioned a leading statistician to conduct a correlation study. Could I actually predict how many books I’d sell by simply looking at my Amazon rankings?
The answer is a resounding “Yes, Yes, Oh God, YES!” (my quote, not the statistician’s). The correlation was, in his words, “Extremely high.” Now, I am not going to pretend that I understand statistics. The most advanced math book I own is called, Subtraction: Addition’s Tricky Friend. But it helps to understand…
How Amazon Comes Up With Its Sales Ranking
Let me be clear: No one actually knows the secret sauce to Amazon’s logarithms. Still, there are some learned mathematicians and statisticians who’ve come up with respected theories. I am not one of them. And rather than bloviate about subjects I am not worthy of explaining, I am going to quote from people who do. I asked my statistician to scour the internet for what he thought was the most intelligent, insightful, educated theory of how Amazon’s sales ranking works. He pointed me to Morris Rosenthal at rampant-books.com.
Indeed, it is not only a learned analysis but an understandable one. Keep in mind that this analysis is about printed books (though clearly the principles hold for Kindle ebooks):
Amazon’s sales rank is calculated as a rolling figure. It’s based on sales over a recent period. I can’t remember if the period is 60 or 90 days, though. It is, however, weighted by overall total sales (they put this back in after having dropped it for a couple of years), keeping long-term big sellers afloat even after their sharp sales peaks have leveled out.
Not all books are recalculated with the same frequency. The top 1,000 are recalculated hourly. The next block (up to 100,000, I think) are recalculated weekly, while the rest get checked monthly. However, a sudden burst in sales is enough to force an immediate recalculation on a 100,000+ book. This is probably based on a percentage of overall sales, but that’s just a guess.
- 1 – 10,000 are recalculated every hour.
- 10,001 – 110,000 are recalculated every day.
- Above 110,001 are recalculated once a month.
To begin with, any book which has no assigned sales rank has yet to sell even one copy on Amazon. So, if you’re looking at a book with a sales rank of 4,000,000, then you at least know it has sold at least one copy.
Rosenthal also says that all items are assigned unique rankings. So if you’re listed at an Amazon Sales Rank of 34,385 then there are only 34,384 books selling better than yours, and your book is selling better than approximately 4,000,000 other books. Again, for more details, go to rampant-books.com.
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In the following post I’ll be tying up everything we’ve learned about my Kindle marketing strategy. You won’t want to miss it!