Underneath Product Details, look for the section that says “Amazon Best Sellers Rank.” In the screenshot above, you can see it says “#139 Paid in Kindle Store.”
Now, there are a few things you should know about this Amazon Best Sellers Rank.
First, notice it says “Paid.” If it said “#139 Free in Kindle Store,” that would mean the Kindle version of the book was currently free (like during a KDP Select 5-Day Free Promotion Campaign
It also says “in Kindle Store.” If you’re looking at a print edition of a book on Amazon, it will say “in Books.”
Now that you have the Amazon Bestseller Rank for the book, all you have to do is type it into the Amazon Kindle Sales Calculator above.
If you want to find out how many print copies the book is selling, just click the Paperback or Hardcover edition of the book on Amazon, scroll down to Product Details on that page, and find the Amazon Best Sellers Rank for the print edition. Then just copy and paste that number into the Amazon Book Sales Calculator above, make sure to select “Book” instead of “eBook” for the book type, and click “Calculate Sales.”