Glossary/Retail Media & Commerce/Advertising Cost of Sales (ACoS)
Retail Media & Commerce
Advertising Cost of Sales (ACoS)
Ad spend divided by the sales those ads generated, expressed as a percentage; Amazon's core efficiency metric and the inverse of ROAS.
By Brandon Mina·CEO, BrandPilot AI·Updated November 2026
Short answer
Advertising cost of sales (ACoS) is ad spend divided by the sales those ads generated, expressed as a percentage. For example, $20 in spend producing $100 in sales equals 20% ACoS. It is Amazon Ads' core efficiency metric and the inverse of ROAS. Sellers compare ACoS to profit margins to judge whether campaigns are profitable.