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MER vs ROAS: which number an agency should report

Platform ROAS tells you how an ad platform scores itself. MER tells you how the business did. A client review needs both, clearly labelled.

What each number measures

Platform ROAS is the revenue a platform attributes to its own ads divided by what you spent there. MER is total store revenue divided by total marketing spend, with no attribution at all.

Why they disagree

Each platform counts orders using its own model and window, and platforms often claim the same order. Add three platform ROAS figures together and the claimed revenue can exceed what the store actually took.

  • Different attribution windows and view-through rules.
  • Orders claimed by more than one platform.
  • Orders no platform can see, such as direct or email traffic.

How to use them together

  • Use MER for the question 'is marketing paying for itself overall this month?'.
  • Use platform ROAS to rank ads and ad sets inside one platform.
  • Never add platform ROAS values to build a total.
  • Write the formula, period and currency next to every figure in the report.
Example with made-up numbers: Meta reports 3.0 and Google reports 4.0, but total revenue divided by total spend is 2.4. The 2.4 is the figure to judge the month by; the other two help decide where to move budget.

What to put in the client report

Show MER as the headline, platform ROAS as supporting detail, and say plainly that platform figures overlap. If a number could not be measured, write 'not measured', never zero.

6 min read. Last updated 2026-10-07. Examples use made-up numbers.

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Terms in this guide

MERPlatform ROASAttribution window

Where this shows up in the product

Reports

Client, channel, campaign and product reports where every figure shows its source, formula and update time.

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AI insights

Checks for drops, anomalies, frequency and missing new creatives, explained with numbers you can verify.

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CRO

Signals from orders and GA4 for products, pages and checkout, turned into a list of hypotheses.

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