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ROAS vs ROI vs MER vs ACoS
Teams confuse these metrics and optimize the wrong lever. Use this page to pick the right KPI for each decision layer.
Quick answer: use ROAS for channel execution, MER for blended executive visibility, ACoS for Amazon efficiency, and ROI for final profitability decisions.
Metric Definitions
| Metric | Formula | Best Used For |
|---|---|---|
| ROAS | Revenue / Ad Spend | Channel-level performance optimization |
| ROI | (Profit - Cost) / Cost | Business-level profitability analysis |
| MER | Total Revenue / Total Marketing Spend | Blended performance across all channels |
| ACoS | Ad Spend / Ad Revenue | Amazon-focused efficiency tracking |
Quick Conversion Rules
- ROAS = 1 / ACoS (if ACoS is in decimal form).
- ACoS = 1 / ROAS.
- High ROAS can still mean poor ROI if margins are low.
- MER can hide weak channels because it blends winners and losers.
Decision Framework
- Use ROAS for campaign-level bid and budget adjustments.
- Use ACoS when managing Amazon Sponsored Products.
- Use MER for weekly executive reporting across channels.
- Use ROI when deciding whether a program should continue at all.