Amazon ACoS vs CPA

Amazon does not report CPA. It reports ACoS: advertising cost of sales, ad spend divided by ad-attributed sales revenue. The mapping is direct: ACoS is the inverse of ROAS, and implied CPA equals ACoS times average order value. A 25% ACoS on $60 orders is a $15 CPA.

ACoS definition: ad spend ÷ ad-attributed sales▸Amazon · checked 2026. Equivalent identities: ACoS = 1 ÷ ROAS; ROAS = AOV ÷ CPA.

• ACoS to CPA: 25% ACoS × $60 AOV = $15 per order. Spend side check: $15 spend per $60 sale is indeed 25%.
• CPA to ACoS: a $20 CPA target on an $80 AOV is 20 ÷ 80 = 25% ACoS. Hand that to the Amazon console as the target.
• Break-even ACoS = gross margin. At 35% margin, ads break even at 35% ACoS: spend equal to your margin consumes exactly the profit. Same ceiling logic as break-even CPA, in Amazon's units.

Amazon sponsored ads are auction CPC against high-intent product searches where the conversion is an on-platform sale with a known price. When every conversion carries revenue, a revenue-relative metric is strictly more informative than a flat per-unit cost, so the console leads with ACoS (and TACoS, which divides by total sales including organic). Off Amazon, conversions vary in kind, so CPA won. Translate rather than argue: run targets through CPA vs ROAS and read the ecommerce framing on the ecommerce benchmark page. No ACoS averages appear here: Amazon publishes definitions, not benchmarks, and the register records that absence.