Each platform’s ROAS tells part of the story, and each platform credits itself. MER (marketing efficiency ratio) divides total revenue by total marketing spend. It is less precise by channel but more honest for the business’s budget decisions.
The essentials in a definition
MER (marketing efficiency ratio) divides total revenue by total marketing spend, without depending on channel attribution. It gives a global, stable view, useful for budget decisions when platforms and measurement diverge. Models such as Meridian and studies such as those from Think with Google help go beyond the global indicator.
What MER is
It is the ratio between the business’s total revenue and total marketing spend in a period. It does not depend on attribution: it uses real invoicing and expense figures. It shows whether investment, as a whole, is earning.
It is a measure of business health, not of campaign optimisation.
Why it complements ROAS
Each platform reports its own ROAS with its own attribution rules, and the sum of ROAS often exceeds real revenue, because several platforms claim the same sale. MER avoids that overlap.
When MER falls while the platforms’ ROAS look good, there is over-attribution or demand is falling.
Using MER alongside ROAS
- Calculate total revenue over total spend
- Set a target MER linked to margin
- Use MER for the overall budget
- Use ROAS to optimise within each platform
How to use it
Track MER weekly and monthly, by product or business line if possible. Set a target MER linked to margin and maximum acquisition cost. Use it to decide the overall budget; use ROAS and cost per conversion to optimise within platforms.
Watch the variations: if MER holds as spend rises, there is room to scale; if it falls, saturation has been reached.
When every platform claims the same sale, only the total tells the truth.
Limits
MER mixes new and returning customers, organic and paid. It may be inflated by sales unrelated to ads. Complement it with cost per new customer and margin.
Use it as a compass, not as a detailed map.
Decision table
| Metric | Calculation | Limit |
|---|---|---|
| Platform ROAS | Attributed revenue ÷ platform spend | Depends on attribution |
| MER | Total revenue ÷ total marketing spend | Does not show channels |
| Contribution MER | (Revenue − variable costs) ÷ spend | Closer to profit |
| Global cost per new customer | Total spend ÷ new customers | Needs good classification |
Common mistakes to avoid
- Using only MER. It hides which channels work; combine with tests.
- Ignoring brand or seasonality effects. They can inflate MER unrelated to campaigns.
- Not separating new customers. Revenue from existing customers distorts efficiency.
How to measure the result
Track weekly and monthly MER, contribution MER and the evolution of total spend, comparing with incrementality tests.
Limits and exceptions
MER is an aggregate indicator: it does not say which channels or campaigns work, and is affected by promotions, seasonality, prices and brand effects. In businesses with long cycles or many offline sales, the weekly reading is noisy. Use moving averages, define the formula and keep it, and complement with channel analysis and experiments.
Illustrative example
Illustrative example: a brand tracks weekly MER and sees it fall when spend on one campaign rises, even though the platform shows an excellent ROAS. It runs a holdout test and confirms part of attributed sales would have happened anyway. It reduces spend on that campaign and MER recovers.
In practice: checkpoints
Calculate MER every week with the same method and use it as a thermometer, not as a replacement for channel metrics. Compare it with contribution margin, and investigate when MER holds but new-customer revenue falls, since it can hide a shift from acquisition to existing customers. Keep a note of promotions, price changes and seasonality next to the series, so movements in the ratio can be explained and not only observed.
Frequently asked questions
Does MER replace ROAS?
No. It complements it. One serves the overall budget, the other optimisation.
Can I calculate it by product?
Yes, if you have revenue and spend by business line.
What MER should I have?
One consistent with your margin and maximum acquisition cost.
Does MER replace ROAS?
No; it complements it, giving a global view that does not depend on each platform’s attribution.
Which spend goes into MER?
All relevant marketing spend: ads, creators, tools and production, per the definition you set.
MER shows overall marketing efficiency without depending on attribution; use it for budget decisions, combined with tests that identify what each channel adds.
Sources and recommended reading
Last editorial review: October 2026. Informational content; always confirm current conditions in the official sources before deciding.