A Quick Way to Calculate Amazon Sales from Rank

Want to know how many sales a given Amazon Kindle rank represents? Here’s a quick and dirty formula:

100,000/rank # = sales per day

In other words, if a book’s rank is #100, then 100,000/100 = 1000 sales/day. If a book’s rank is #1000, then 100,000/1000 = 100 sales/day. At #100,000, then 100,000/100,000 = 1/day.

The formula breaks down at the extremes. It probably overestimates the sales of the top 100 books by a little, and the #1 book in a given day probably sells much more like 10,000/day than 100K, although as ever, at the top, it varies tremendously. And at #1,000,000, that’s not a book that sells 1 copy/10 days. We’re talking about a book that might not have sold more than 1 copy ever, or at least within the last 6 months.

Overall, though, it’s a pretty good rule of thumb. It’s probably a little conservative–tack on 10-20%, and you’re probably closer to the truth for most ranks–and it also depends on factors like velocity of sales in the last 0-48 hours, so books that have recently been boosted by a sale may be +/- 50% of the sales numbers or more. Also, a book that has hung out at a certain rank for a while needs fewer sales to maintain that ranking long-term.

Treat it as a guideline, though, and it’s pretty close to the truth. Does that mean you could extrapolate it to estimate how many ebooks Amazon sells per day? Yes. You totally could.