ROAS vs MER vs POAS: Which Metric Should You Use?
Understand the differences between Return on Ad Spend, Marketing Efficiency Ratio, and Profit on Ad Spend—and when to use each metric.
• ROAS: Best for campaign optimization, but inflated by attribution overlap (10-40%)
• MER: Most reliable for overall marketing efficiency, not affected by attribution issues
• POAS: Best for profitability analysis, accounts for margins (ROAS 1.0 ≠ profitable)
• Use all three: ROAS for tactics, MER for strategy, POAS for profitability
€40,000 revenue ÷ €10,000 ad spend = 4.0 ROAS
Pros
- • Easy to calculate
- • Platform-reported
- • Campaign-specific
Cons
- • Inflated by attribution overlap
- • Doesn't account for margins
- • Ignores non-ad marketing
Best for: Campaign optimization and platform comparison
€100,000 revenue ÷ €25,000 marketing = 4.0 MER
Pros
- • Blended view across channels
- • Not affected by attribution
- • More reliable than ROAS
Cons
- • Less granular
- • Can't optimize individual campaigns
- • Includes non-ad spend
Best for: Overall marketing efficiency and CFO reporting
€16,000 profit ÷ €10,000 ad spend = 1.6 POAS (40% margin)
Pros
- • Accounts for profitability
- • Shows true ROI
- • Prevents margin blindness
Cons
- • Requires margin data
- • More complex to calculate
- • Not platform-reported
Best for: Profitability analysis and budget allocation
Use ROAS When:
- • Optimizing individual campaigns or ad sets
- • Comparing performance across platforms (Meta vs Google)
- • Making tactical decisions about budget allocation
- • Testing new creative or audiences
⚠️ Warning: Platform-reported ROAS is inflated by 10-40% due to attribution overlap. Always reconcile with Shopify revenue.
Use MER When:
- • Reporting to CFO or leadership team
- • Evaluating overall marketing efficiency
- • Making strategic decisions about total marketing budget
- • Comparing performance month-over-month or year-over-year
✅ Advantage: MER is not affected by attribution models or platform discrepancies. It's your single source of truth.
Use POAS When:
- • Analyzing true profitability of campaigns
- • Comparing products with different margins
- • Determining break-even performance
- • Making decisions about scaling or cutting campaigns
💡 Pro tip: POAS = ROAS × Gross Margin %. A 4.0 ROAS with 40% margin = 1.6 POAS (60% profit).
Scenario: E-commerce Brand Running Meta + Google Ads
Meta reports: €50,000 revenue, €10,000 spend = 5.0 ROAS
Google reports: €40,000 revenue, €8,000 spend = 5.0 ROAS
Shopify actual revenue: €70,000 (not €90,000!)
Total marketing spend: €20,000 (ads + email + influencers)
COGS: €42,000 (60% margin)
Platform ROAS: 5.0 (inflated by 29% attribution overlap)
True ROAS: 3.9 (€70k ÷ €18k ad spend)
MER: 3.5 (€70k ÷ €20k total marketing)
POAS: 1.6 (€28k profit ÷ €18k ad spend)
This brand is profitable (POAS 1.6 = 60% profit margin), but platform ROAS over-reports performance by 29%. MER shows the true marketing efficiency across all channels.