ACOS formula: ad spend ÷ attributed ad sales × 100. ROAS formula: attributed ad sales ÷ ad spend. If ACOS is 25%, ROAS is 4.0×. They are inverse views of the same advertising ratio.
Amazon ACOS example
If a campaign spends $500 and produces $2,000 in attributed sales, ACOS is 25%. The advertiser spent twenty-five cents in advertising for each attributed sales dollar.
Amazon ROAS example
Using the same campaign, $2,000 divided by $500 equals 4.0. The campaign generated four dollars in attributed sales for every advertising dollar spent.
ACOS and ROAS conversion table
| ACOS | ROAS | Interpretation |
|---|---|---|
| 10% | 10.0× | $10 attributed sales per $1 spend |
| 20% | 5.0× | $5 attributed sales per $1 spend |
| 25% | 4.0× | $4 attributed sales per $1 spend |
| 33.3% | 3.0× | $3 attributed sales per $1 spend |
| 50% | 2.0× | $2 attributed sales per $1 spend |
What is a good ACOS?
There is no universal good ACOS. A viable target depends on product margin, Amazon fees, fulfillment, returns, taxes, lifecycle stage, and the objective of the campaign. A launch campaign may intentionally accept a higher ACOS than a mature profitability campaign.
Calculate break-even ACOS
Break-even ACOS is approximately the contribution margin available before advertising, expressed as a percentage of selling price. If a $40 product has $12 remaining after product cost, Amazon fees, fulfillment, shipping, and variable costs, the pre-ad contribution margin is 30%. An ACOS above 30% would generally consume that contribution before considering overhead.
This is a simplified model. Returns, promotions, tax treatment, cross-ASIN purchases, and lifetime value can change the economic result.
Why ACOS can mislead
- It considers attributed advertising sales, not total account sales.
- Attribution windows mean recent performance may still change.
- A low ACOS can hide lost growth if profitable campaigns are budget constrained.
- A high ACOS may be intentional during a controlled launch or ranking strategy.
- Different products can have very different margins at the same ACOS.
Use ACOS, ROAS, and contribution together
Operational teams often find ACOS intuitive for setting efficiency limits, while finance teams may prefer ROAS for comparing channels. Use both with contribution margin, total sales, TACOS where reliable total-sales data exists, inventory position, and campaign purpose.