ROAS vs ACoS — what's the difference?
Same underlying data, different conventions. Google Ads and Meta optimize on ROAS (revenue per ad dollar). Amazon Advertising reports ACoS (ad cost per revenue dollar). Knowing the conversion is non-negotiable if you run cross-platform.
ROAS (Return On Ad Spend)
Revenue generated for every $1 of ad spend.
When to use: Google Ads, Meta, TikTok, programmatic. Optimizing toward a value-based bidding target.
ACoS (Advertising Cost of Sale)
Ad spend as a percentage of revenue. The exact inverse of ROAS.
When to use: Amazon Advertising, marketplace PPC, retail-media buying.
Bottom line
ACoS = 1 ÷ ROAS, expressed as a percentage. A 4:1 ROAS = 25% ACoS. Translate, don't argue with the platform.
Frequently asked
What's a good ACoS on Amazon?
Below your gross margin, with headroom. Selling a product at 35% gross margin? 25% ACoS is healthy, 30% is break-even-ish, 40% is losing money.
Why does Amazon use ACoS instead of ROAS?
Because in retail PPC, sellers think in cost-of-sale percentages (like wholesale margin), not revenue multiples. Same math, different industry vernacular.