#ACOS #Amazon Ads #KDP #metrics #Sponsored Products
What Is ACOS and How to Calculate It (With Examples)
James Whitfield · July 23, 2026 · 6 min read
ACOS (Advertising Cost of Sales) is the percentage of your advertising revenue that you spend on advertising. You calculate it by dividing ad spend by ad sales and multiplying by 100. If you spent $25 on ads and those ads produced $100 in sales, your ACOS is 25%.
That single number is the fastest way to tell whether an Amazon Ads campaign is making you money or quietly draining it. This guide explains what ACOS means, how to calculate it, what a "good" ACOS looks like for a KDP book, and the mistakes that make the number lie to you.
The ACOS formula
ACOS = (Ad Spend / Ad Sales) x 100
- Ad Spend is the total you paid Amazon for clicks in a given period.
- Ad Sales is the revenue Amazon attributes to those ads in the same period.
A worked example
In one week your Sponsored Products campaign records:
- Ad Spend: $40
- Ad Sales: $160
ACOS = (40 / 160) x 100 = 25%
That means for every $1 of sales the ads generated, you spent 25 cents on advertising. You can run these numbers instantly with the free ACOS calculator.
What is a good ACOS for a KDP book?
There is no universal "good" number, because it depends entirely on your margin. The honest way to think about it: your break-even ACOS equals your profit margin. Below that number you make a profit on the ad; above it you lose money to acquire the sale.
For a Kindle eBook the math is generous, because royalties are high. For a paperback it is much tighter, because printing eats most of the price.
| Format | Price | Royalty | Break-even ACOS |
|---|---|---|---|
| Kindle eBook | $4.99 | ~70% ($3.49) | ~70% |
| Paperback | $12.99 | ~$3.20 after print | ~25% |
| Hardcover | $24.99 | ~$5.50 after print | ~22% |
So a 45% ACOS can be highly profitable on a Kindle eBook and a disaster on a paperback. Never judge the number without knowing the margin behind it.
ACOS vs ROAS vs TACOS
These three metrics describe the same relationship from different angles:
- ACOS: ad spend as a percentage of ad sales. Lower is more efficient.
- ROAS (Return on Ad Spend): ad sales divided by ad spend, shown as a ratio. It is the inverse of ACOS. A 25% ACOS is a 4x ROAS.
- TACOS (Total ACOS): ad spend as a percentage of total sales, including organic. It tells you how dependent your book is on ads.
Three mistakes that make ACOS lie to you
- Judging it without margin. A "high" ACOS on a high-royalty eBook can still be profitable. Always compare ACOS to your break-even.
- Reading it too early. Amazon attributes sales in a delayed window. A campaign that looks like 90% ACOS on day two often settles far lower once conversions land.
- Optimizing for the lowest ACOS. The lowest ACOS usually comes from the fewest, safest clicks. Chasing it can starve the campaign of the volume that actually grows the book.
How to lower ACOS the right way
Lowering ACOS is not about cutting spend blindly. It is about spending on what converts:
- Move budget from keywords with clicks and no sales to keywords that sell.
- Add the search terms that convert as exact-match keywords, and negate the ones that only cost.
- Adjust bids toward your target ACOS instead of a flat guess.
Doing this by hand across a full catalog is slow and error-prone, which is exactly the work Essentia automates.
FAQ
Is a lower ACOS always better? No. A lower ACOS means each sale is cheaper to acquire, but pushing it too low usually means fewer sales overall. The goal is the ACOS that maximizes profit, not the smallest number.
What is the difference between ACOS and TACOS? ACOS measures ad spend against sales from ads only. TACOS measures ad spend against total sales, including organic. A falling TACOS is a healthy sign that your book is selling on its own, not only through ads.
What ACOS should a new KDP campaign target? Start at your break-even ACOS and give the campaign time to gather data before tightening. For most eBooks that is a comfortable range; for print books, aim well under 30%.
Does a high ACOS hurt my ranking? Not directly. Amazon does not rank you on ACOS. But the sales velocity that advertising drives does help organic ranking, which is why some publishers accept a break-even ACOS to build momentum.