If platform ROAS is the wrong north star (and it is), MER is the replacement. MER is Marketing Efficiency Ratio, total revenue divided by total paid marketing spend, one number per month. It is how operators who actually tie paid social to their P&L run their accounts. This piece covers the specific math, the thresholds, and the reporting rhythm that makes MER work.
The formula
Blended MER equals total revenue divided by total paid marketing spend. That is it. No attribution models, no platform weighting, no lookback window debates. Revenue is the money that landed in your Shopify register. Spend is every dollar you paid to Meta, TikTok, Google, LinkedIn, influencer deals, sponsorships, and anything else with an invoice that was meant to drive revenue.
$300K in Shopify revenue divided by $160K in paid marketing spend is a blended MER of 1.875x. The fact that Meta claims 4.1x ROAS on its share, TikTok claims 2.6x on its share, and Google claims 3.8x on its share is a separate conversation from what the business actually did. Why platform ROAS is the wrong north star covers why the platform claims cannot reconcile to the blended number.
What to include in spend
This is where brands argue themselves out of using MER. The temptation is to exclude certain channels because "they're not really the same as paid social." Resist.
Include in paid marketing spend:
- Platform ad spend (Meta, TikTok, Google, LinkedIn, Pinterest, Reddit, anywhere you buy media)
- Influencer deals paid in cash
- Affiliate payouts
- Sponsorships and brand deals
- Creator gifting at book value
- Email and SMS platform fees (Klaviyo, Attentive, etc.)
- Agency retainers and freelancer media fees (debated but usually include)
Do not include:
- Tool subscriptions that are not channel-specific (Slack, Notion, etc.)
- Salary of internal marketing staff
- Product cost or COGS
The debate usually centers on agency fees. My call: include them. The agency fee is marketing spend directed at producing revenue. Excluding it flatters the MER number and hides the total cost of your marketing operation.
What to include in revenue
Top-line Shopify revenue is the simplest baseline. Some operators argue for net revenue (after returns), gross profit, or contribution margin. All are defensible. My call for most brands: use gross revenue as the top-line MER number and track contribution margin MER separately as a cross-check.
The MER threshold by gross margin
The minimum viable MER depends on your gross margin. Here is the math.
To be profitable on contribution margin, MER must be greater than 1 divided by gross margin percentage. At 50 percent gross margin, you need MER above 2.0. At 35 percent gross margin, you need MER above 2.86. At 25 percent gross margin, you need MER above 4.0.
These are floors, not targets. Below them, you are losing money on every marketing dollar spent. A brand with 40 percent gross margin running MER of 2.0x looks healthy in isolation but is actually losing money on contribution. The floor for that brand is 2.5x. Any MER under 2.5x is unprofitable.
This math is what agencies rarely foreground. Platform ROAS of 4x sounds great until you do the gross margin adjustment and realize the blended math is underwater. Why agencies overspend on top of funnel covers the structural reason this math gets buried.
The monthly reporting rhythm
Every month, produce one page. Top of the page: three numbers.
- Total revenue
- Total paid marketing spend (all channels, invoiced this month)
- Blended MER (revenue divided by spend)
Below that, the comparison: how does this month's MER compare to the last three months, the last six months, and the same month last year? Trend matters more than the spot number.
Below that, the platform diagnostic section. Meta ROAS, TikTok ROAS, Google ROAS. Each labeled clearly as "platform-attributed, diagnostic." Not as the north star. These numbers are there so you can identify which platform is drifting when blended MER moves.
Below that, the incrementality findings if you ran any tests this month. Incrementality is the gold standard, and the case for MER over platform ROAS covers why incrementality is the only way to know a channel's real contribution.
Weekly vs. monthly cadence
Run MER monthly as the primary rhythm. Weekly MER is too noisy for most DTC brands. Events like a single affiliate post, a single viral TikTok, or a single Meta algorithm hiccup can swing weekly MER by 30 percent without representing a real business change. Monthly smooths the noise.
If you are running at $500K+/month paid spend, biweekly MER starts making sense because the sample size is larger. Still not weekly.
Breaking down MER by campaign stage
Blended MER is the whole-business number. It hides important detail. A useful secondary cut: MER by campaign stage.
- TOF MER: revenue attributed to top-of-funnel cohorts divided by TOF spend
- MOF MER: revenue attributed to middle-of-funnel audiences divided by MOF spend
- Retargeting MER: revenue from retargeting cohorts divided by retargeting spend
These cuts require a warehouse or at least honest attribution modeling in a BI tool. Platform ROAS per campaign stage is not the same thing because it still relies on platform attribution claims. The cleanest version uses a warehouse-based attribution model that reconciles first-party session data with Shopify orders.
“MER is the only paid social number that survives the translation to a board meeting. Platform ROAS does not. If your metric cannot be explained to a non-marketer in 30 seconds, it is the wrong metric.
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The CAPI connection
Blended MER does not care about CAPI quality in its top-line formula. Your revenue number is your revenue number. But the platform-level diagnostics you use to investigate MER movements depend entirely on CAPI quality. If Meta's reported ROAS is moving because match quality is dropping, you cannot tell the difference between a genuine performance problem and a measurement problem without clean CAPI. Wiring CAPI signal back into the creative testing loop covers the CAPI side of this work.
The trap operators fall into
The trap is this: once you start measuring on MER, the platform ROAS numbers look bad, and the temptation is to explain them away. "Our Meta ROAS is down but that's because iOS 17 hit harder this quarter." "TikTok ROAS looks weak but the brand lift from TikTok isn't captured." "Google ROAS dropped because Performance Max isn't giving us visibility."
These may all be true. They may all be rationalizations. The MER number is what it is. It went up or it went down. Investigate the platform numbers as diagnostics, but do not let the diagnostic story override what MER is telling you. If MER is down three months in a row, the business is becoming less efficient, regardless of what the platform ROAS explanations say.
Should I include email revenue in my MER denominator?
Include Klaviyo/Attentive platform fees in spend. Email revenue is already captured in total revenue in the numerator. The question is whether you attribute email-driven purchases separately from paid social purchases. For MER, you do not need to. The blended formula does not care which channel the conversion came through.
What if I have a high-LTV subscription business?
For subscription businesses, calculate MER on first-order revenue and track LTV:CAC separately. Using total lifetime revenue in the MER numerator overstates current-period efficiency because you are counting future revenue against current spend.
Does MER work for very small brands under $500K annual revenue?
Yes, but the monthly variance is higher because sample sizes are smaller. Use 3-month rolling MER instead of spot monthly at smaller scales.
Related reading
This piece is part of the paid social for DTC operators hub. The contrarian case against platform ROAS is ROAS is the wrong north star. The structural reason agencies rarely lead with MER is why most agencies overspend on top of funnel. For the measurement stack that makes MER diagnostics trustworthy, the DTC Stack Audit runs the CAPI, analytics, and data-layer checks together.