The numbers below are based on MY experiences... I'm sure you can find other authors whose numbers are different from these...but the following s/b pretty darn close.
The rankings are interesting to look at if you have a book out there and you are hoping to, for example, get on the Top 100 Romantic Suspense Bestsellers List on Amazon. If I look at the Romantic Suspense List and click on the book title of #99 or #100 and that book has a Bestsellers Rank of 3,400, then I know I need a 3,399 or better to get on that list. ABDUCTED was #93 for about an hour last night.
Amazon Bestsellers Rank is the number you find beneath the Product Description. Every book on Amazon has an Amazon Bestsellers Rank. Click on any title and then scroll down until you see it.
Bestsellers Rank 40,000 to 100,000 - selling close to 1 book a day. (per kindleboards)
Bestsellers Rank 8,500 to 40,000 - selling 1 to 10 books a day.
Bestsellers Rank 3,500 to 8,500 - selling 10 to 20 books a day.
Bestsellers Rank 1,500 to 3,500 - selling 20 to 40 books a day.
Bestsellers Rank 1,100 to 1,500 - selling 40 to 50 books a day.
Bestsellers Rank 900 to 1,100 - selling 50 to 65 books a day.
Bestsellers Rank 650 to 900 - selling 65 to 85 books a day.
Bestsellers Rank 450 to 650 - selling 85 to 100 books a day.
Bestsellers Rank 350 to 450 - selling 100 to 200 books a day.
Bestsellers Rank 100 to 350 - selling 200 to 300 books a day.
Bestsellers Rank 68 to 100 - selling 300 to 700 books a day.
Bestseller Rank of 59 to 68 - selling 700 to 740 books a day.
Bestseller Rank of 3 to 8 - selling about 4,000+ books a day!
That's all I've got for now. If you have more information, please share. And if you see an error, I will fix it. Thanks.