What is Amazon BSR?
Best Seller Rank is Amazon's rolling measure of recent sales velocity for every book in the Kindle and Print stores. Rank #1 sells thousands of copies per day; rank #1,000,000 may sell one copy per month. BSR updates hourly and is heavily weighted toward the past 24 hours, so a single spike (free promo, BookBub feature) can move rank dramatically.
Why BSR estimates are approximations
Amazon never publishes the BSR-to-sales formula. Industry estimates (including this one) are built from author-disclosed data and reverse-engineered observation. Use BSR estimates as a relative gauge — 'this niche has competitors selling 50/day' — not an exact unit forecast.
Using BSR for niche research
Before writing in a niche, check the top 20 BSRs in the target sub-category. If the #20 book is ranked 100,000+, the niche is too quiet. If the top 5 are all under 5,000 BSR, the niche is hot but probably competitive. A healthy sweet spot is top-20 BSRs between 10,000 and 50,000 — enough demand to support new entrants.
BSR vs sub-category rank
Overall BSR competes against millions of books. Sub-category rank (e.g. #3 in 'Cozy Mysteries') is a marketing asset — Amazon shows the top 100 in each sub-category. Aim for #50 or better in two relevant sub-categories during launch; the badge boosts conversion.
Frequently asked questions
How accurate are BSR estimates?
Within ±50% at high ranks, more accurate (±20%) for ranks under 10,000 where data is plentiful.
Why does my BSR change every hour?
Amazon recalculates rolling sales velocity hourly. A single sale can move a 200,000-ranked book to 50,000 temporarily.
Is lower BSR always better?
Yes — BSR #100 outsells BSR #10,000. Sub-category rank can be different (you can be #1 in a sub while overall BSR is 50,000).
Does BSR include KU borrows?
Yes — KU borrows count toward BSR similarly to paid sales.