About the CPA Calculator
Cost per acquisition (CPA), also called cost per sale or cost per order, is how much advertising it took to win one sale. If you spent $150 and the ads produced 40 sales, each sale cost $3.75 in ads.
For authors, CPA is the most intuitive way to judge an ad: you can compare it directly with your royalty per sale. If a sale costs $3.75 in ads and pays you $4.99, you keep $1.24. If it costs $6.00, you lose about $1.01 on every ad-driven sale, no matter how good the ACOS or ROAS looks.
CPA also links the other ad metrics together. It equals your average CPC divided by your conversion rate, so you can lower it either by paying less per click or by converting more of those clicks into orders.
How It Works
CPA is ad spend divided by the number of conversions (orders) the ads produced.
If you add your royalty per sale, profit per sale is royalty minus CPA. A negative figure is the loss on each ad-driven sale.
Conversions must be a whole number greater than zero. Use orders, not units, if one order can contain several copies and you want cost per customer.
Formula
- CPA
- CPA = Ad spend ÷ Conversions
- Also equal to
- CPA = Average CPC ÷ Conversion rate
- Profit per sale
- Profit per sale = Royalty per sale − CPA
Example
$150 spend, 40 sales, $4.99 royalty per sale
- CPA: $150 ÷ 40 = $3.75.
- Profit per sale: $4.99 − $3.75 = $1.24.
Each ad-driven sale costs $3.75 and earns $4.99, leaving about $1.24 of profit per sale.
Important Notes
- Profit per sale covers ad cost only. Editing, cover design and other fixed costs are not included.
- Kindle Unlimited borrows and page reads are not counted as conversions.
- Sales of other books in a series after the first purchase are not included, which can make CPA look worse than the true return.
- Recent CPA can drop as late-attributed orders are added to your ad reports.
Frequently Asked Questions
What is the difference between CPA and CPC?
CPC is the cost of one click. CPA is the cost of one sale. Since only some clicks buy, CPA is CPC divided by conversion rate. A $0.40 CPC with a 10% conversion rate gives a $4.00 CPA.
What is a good CPA for a book?
Any CPA below your royalty per sale is profitable on that sale. If you want a margin, set a target such as royalty minus $1.00 and keep CPA under it.
Can a CPA higher than my royalty ever make sense?
Sometimes, for first-in-series books where readers go on to buy later books, or during a launch where rank and reviews matter. Be deliberate and track total royalties to confirm it pays off.
How do I lower CPA?
Reduce bids on targets that click but rarely buy, pause clear losers, and improve conversion on your product page. Either lower CPC or higher conversion rate will bring CPA down.
Where do I find conversions?
In your Amazon Ads reports, usually shown as Orders for the campaign and date range. Use the same range as your spend.
Related KDP Tools
- CPC CalculatorCalculate average cost per click from spend and clicks.
- Conversion Rate CalculatorCalculate the share of clicks or page visits that turn into orders.
- KDP Ad Profit CalculatorModel clicks, conversions and royalty to see whether your Amazon Ads campaign makes money.
- ACOS CalculatorCalculate Advertising Cost of Sale, plus break-even and target ACOS for books.
- Advertising Break-Even CalculatorFind your break-even CPC, break-even ACOS and maximum sustainable bid.
- TACOS CalculatorMeasure ad spend against total sales, including organic, to see true ad dependency.