Here’s an interesting chart I ran across in David Gaughran’s book, “Let’s Get Visible.” If you haven’t read his book, I highly recommend it. The chart serves as a guideline for estimating how many sales are required for an eBook to make it on the Best Seller List in the Amazon US store.
Rank to Sales Estimator
#1 to #5 = 3,500+ books a day (sometimes a lot more)
#5 to #10 = 2,000 to 3,500 per day
#10 to #20 = 1,100 to 2,000
#20 to #65 = 850-1,100
#80 = 850
#90 = 750
#275 = 325
#500 = 200
#1000 = 100
#2000 = 50-55
#3000 = 40-45
#4000 = 30
#5000 = 20-25
#7500 = 16
#12000 = 10
#25000 = 5
#32000 = 3
#42500 = 2
#70000 to #100,0000 = 1
#1000,000+ = less than 1 per day