Short answer: MER (marketing efficiency ratio) is total revenue divided by total ad spend across every platform for the same period. Blended ROAS is the same idea, usually limited to paid channels. It cannot be inflated by platforms double-counting the same sale, so it is the most honest single number for a client who advertises in more than one place.
The problem MER solves
Imagine a client spends on Meta, Google and TikTok. Each platform reports its own ROAS, and each one counts a sale if its ad was involved inside its attribution window. When a customer saw a TikTok video, clicked a Meta ad and finally bought through a Google search, all three platforms can claim that same sale.
Here is an illustrative month (made-up numbers, for the example only):
| Source | Spend | Revenue claimed | ROAS |
|---|---|---|---|
| Meta Ads | $6,000 | $21,000 | 3.5 |
| Google Ads | $4,000 | $16,000 | 4.0 |
| TikTok Ads | $2,000 | $5,000 | 2.5 |
| Platforms added up | $12,000 | $42,000 | 3.5 |
| Store (actual) | $12,000 | $30,000 | MER 2.5 |
The platforms claim $42,000 between them. The store took $30,000. If the report only shows platform ROAS, the client believes they are getting 3.5 back for every dollar when the business is actually getting 2.5, and that includes revenue from returning customers who might have bought anyway.
How to calculate MER and blended ROAS
- MER = total revenue (from the store or CRM) ÷ total ad spend (all platforms).
- Blended ROAS = revenue attributed to paid channels ÷ total ad spend. Some teams use GA4 paid-channel revenue here; some use the same store figure as MER.
- aMER or new-customer MER = revenue from first-time customers ÷ total ad spend. Useful when the client cares most about growth rather than repeat orders.
Use the same date range for spend and revenue, use revenue net of refunds if the client can provide it, and decide whether tax and shipping are included. Then write the definition in the report footnote and do not change it without saying so.
Setting a target: start from break-even
An MER means nothing without the client's margin. A quick way to set the floor:
Break-even MER = 1 ÷ gross margin. With a 40% gross margin, break-even is 1 ÷ 0.4 = 2.5. Below 2.5, ads are not paying for the products they sell, before any other costs.
From there, agree a target with the client that leaves room for overheads and profit, or a deliberately lower target during a growth push when lifetime value justifies it. This turns "is 2.8 good?" into a question the client can answer with you.
Where MER fits in the report
Put it at the top, next to total spend and total revenue, because it answers the question the client actually has: "is the money I put into ads coming back?" Then use platform sections underneath for decisions:
- Summary: total spend, total revenue, MER, change against last period and against target.
- Platform sections: each platform's own ROAS or CPA, used to decide where budget goes next.
- Creatives: the ads to scale, keep or cut.
- Next steps: what changes this period.
When MER can mislead
- Organic spikes. A press mention, an email launch or a viral post lifts revenue without ads, and MER looks better than the ads deserve. Note big non-paid events in the report.
- Brand-heavy search. If most Google spend is on brand terms, it captures demand created elsewhere. MER will look healthy while growth is flat.
- Short periods. Weekly MER is noisy, especially for high-priced products. Show it weekly if you like, but judge it monthly.
- Lead generation. If the client sells offline, revenue arrives weeks later. Use cost per qualified lead or pipeline value instead, and add MER once the CRM can supply closed revenue.
What to tell the client
"Each ad platform takes credit for any sale its ads touched, so their numbers overlap. MER uses only your real revenue and your total ad spend, so it cannot be inflated. We use it to judge the whole programme, and each platform's own numbers to decide where to move budget."
Adsorra puts total spend across Meta, Google, TikTok, LinkedIn, Microsoft, Pinterest and Snapchat in one report so the blended picture sits above the platform detail. See the integrations, or read the metrics glossary for the other formulas.
Frequently asked questions
What is a good MER?
It depends on margins. Work out break-even first: if your gross margin is 50%, an MER of 2.0 covers product costs and ad spend before other overheads. The target should come from the client's margins, not from an industry average.
Is MER the same as blended ROAS?
They are close and often used interchangeably. MER usually divides all revenue by all ad spend. Blended ROAS sometimes uses only revenue attributed to paid channels. Define which one you use in the report.
Should I stop reporting platform ROAS?
No. Platform ROAS is still the best tool for decisions inside each platform. MER sits above it as the business-level check.