What it means
ACoS (Advertising Cost of Sale) is a central Amazon Ads metric comparing ad spend to ad-attributed revenue: ACoS = (ad spend ÷ attributed revenue) × 100. An ACoS of 30% means you spend 30 cents per euro of ad revenue. Whether an ACoS is 'good' depends on your margin: if ACoS exceeds your pre-advertising margin, every advertised sale loses money (break-even ACoS = margin). A deliberately higher ACoS can still make strategic sense during product launches or to build organic ranking.