Blended ROAS and MER: Why Your Ad Platforms All Claim the Same Sale
Add up what Meta, Google and TikTok each say they generated and you'll often get a number larger than your actual revenue.
That isn't a bug and nobody's lying. It's a structural feature of how attribution works — and it's why platform ROAS should never be the number you make decisions on.
Why do the platforms over-count?
Each platform only sees its own contribution, and claims the whole sale.
A customer sees your Meta ad on Monday, searches your brand on Google on Wednesday, and buys on Friday. Meta claims that sale. Google claims that sale. You had one sale.
Three things make it worse:
Overlapping attribution windows. Meta might count a purchase within 7 days of a click; Google similar. Any journey touching both gets counted twice.
View-through attribution. Meta can count a conversion from someone who saw the ad without clicking. Reasonable in principle — but that customer may have been coming anyway.
Branded search. Google gets credit for people searching your brand name. Those people already knew about you; something else did the work.
The result: the sum of platform-reported revenue routinely exceeds real revenue, sometimes by a wide margin, and it's worst when you run multiple channels — the exact situation where you most need to compare them.
What is blended ROAS?
Total revenue divided by total ad spend, across everything.
Blended ROAS = Total revenue ÷ Total ad spend (all platforms)It can't over-count, because both numbers are actual. Revenue comes from Shopify, spend from your bank.
Compare:
| Reported | |
|---|---|
| Meta says | $28,000 from $7,000 (4.0x) |
| Google says | $19,000 from $4,000 (4.75x) |
| TikTok says | $6,000 from $2,000 (3.0x) |
| Platforms total | $53,000 from $13,000 (4.1x) |
| Actual Shopify revenue | $41,000 |
| Blended ROAS | $41,000 ÷ $13,000 = 3.15x |
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The platforms claim 4.1x. Reality is 3.15x. If your break-even ROAS is 3.33 — which corresponds to a 30% contribution margin — you are losing money while every dashboard shows you winning.
What is MER?
Marketing Efficiency Ratio — the same idea, and in practice the same calculation:
MER = Total revenue ÷ Total marketing spendSome people include costs beyond paid ads — agency fees, influencer payments, content production. That's arguably more honest, since those are real acquisition costs.
The important thing isn't the label. It's that you're dividing real revenue by real spend, rather than trusting numbers each platform generated about itself.
Should I ignore platform ROAS entirely?
No — use it for the right job.
Platform ROAS is useful for relative comparison inside one platform. Which Meta creative beats which other Meta creative? Platform data answers that fine, because the bias applies equally to both.
Blended ROAS and MER are for decisions about the business. Are we spending too much overall? Can we afford to scale? Are we actually profitable?
The mistake is using platform ROAS for the second category — comparing Meta's 4.0x to Google's 4.75x and shifting budget accordingly. Those numbers aren't measured the same way and aren't comparable.
What's a good blended ROAS?
It depends entirely on your contribution margin. Break-even blended ROAS is:
1 ÷ contribution margin %At 30% margin you need 3.33x to break even. At 50%, 2.0x.
Which is why a blanket "aim for 4x ROAS" is meaningless advice. For some stores 4x is comfortable; for others it's a slow loss. See how to tell when you're spending too much.
What about organic sales inflating my blended number?
A fair objection. Blended ROAS includes revenue that would have happened without any advertising — repeat customers, direct traffic, organic search.
Two ways to handle it:
Track the trend, not the level. If blended ROAS is falling while spend rises, your marginal ad spend is getting worse, regardless of what the organic baseline is.
Watch new-customer ROAS. Total revenue from first-time customers divided by ad spend removes the repeat-purchase flattery, and is closer to a true acquisition measure.
Neither is perfect. Both beat adding up what the platforms claim.
The practical version
Monthly, take five minutes:
- Total revenue from Shopify
- Total ad spend across every platform, from your actual invoices
- Divide
- Compare against your break-even ROAS
- Note the direction of travel versus last month
The friction is step 2 — logging into three platforms and reconciling different date ranges and currencies. It's why most owners do this twice and stop.
Automating exactly that is a large part of why we built Rev Room: blended ROAS and MER across Meta, Google and TikTok alongside true contribution margin for NZ and Australian Shopify stores, so the comparison against break-even is continuous rather than an occasional manual exercise.
The short answer
- Platforms each claim the whole sale, so their totals exceed reality
- Blended ROAS = total revenue ÷ total ad spend. It can't over-count
- MER is the same idea, often including non-ad marketing costs
- Use platform ROAS inside a platform, blended for business decisions
- Break-even blended ROAS = 1 ÷ contribution margin — everything depends on that number
Related reading: How do you know when you're spending too much? · How to calculate your profit margin properly · When should you be running Meta ads?
General information only, current as at 20 August 2026. Figures are illustrative.