Operator glossary
ACoS (Advertising Cost of Sale)
Ad spend divided by ad-attributed revenue for a campaign or account — the standard Amazon ads efficiency ratio, and the easiest one to over-optimize.
ACoS is the ratio Amazon's console puts in front of you: spend ÷ ad-attributed sales. A 25% ACoS means $1 of ads bought $4 of tracked ad revenue. It is the right lens for comparing campaigns and bids against each other, and the wrong lens for judging the whole account, because it ignores every organic sale the ads helped create.
The classic failure mode is managing the account to the prettiest possible ACoS: brand-defense terms and retargeting look great, incrementality-heavy work looks bad, so the budget migrates to ads that harvest demand instead of creating it. Pair ACoS with TACoS and the distortion disappears.
The numbers
- ACoS = ad spend ÷ ad-attributed sales; its inverse is ROAS (25% ACoS = 4.0 ROAS).
- Attribution windows differ by ad type (14-day click for Sponsored Products), so console ACoS keeps moving for days after the click.
- Commonly cited cross-category averages sit near 30%, but spread is wide enough that only your own break-even number is decision-grade.
Primary sources: Amazon Ads glossary
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