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.

TL;DR: The Key Differences

• 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

ROAS
Revenue ÷ Ad Spend

€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

MER
Total Revenue ÷ Total Marketing Spend

€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

POAS
Profit ÷ Ad Spend

€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

When to Use Each Metric

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).

Real-World Example
Why all three metrics tell different stories

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.

Related Calculators
Calculate your ROAS, MER, and POAS with our free tools