MER
MER, the Marketing Efficiency Ratio, is a company's total revenue divided by its total marketing spend over the same period. Unlike campaign-level ROAS it does not care which conversion got credited to whom, which is why attribution cannot fool it. It is the owner's view: how much revenue every unit of overall marketing spend brought in. Blended ROAS calculates practically the same thing, sometimes narrowed to ad spend only; the two are used interchangeably.
In short
| Formula | MER = total revenue / total marketing spend |
| How it differs from ROAS | ROAS measures a campaign by credited conversions. MER measures the company by its books |
| Strength | Cannot be distorted by attribution, duplication or measurement changes |
| Weakness | Says nothing about which channel drives the result. That is what incrementality tests are for |
How it is calculated
Formula and inputs
MER = total revenue / total marketing spend over the same period. The numerator is the whole company's revenue as recorded in the books: from all channels including organic, direct and repeat purchases, net of VAT and after cancellations and returns. It is not the revenue credited to campaigns inside platforms. The denominator holds everything the company spends on marketing: media spend on all platforms, agency fees, measurement and management tools, creative and content production, affiliate commissions and influencer fees. In-house marketing salaries are either included or not; the decision is made once and kept. The calculation runs by calendar month, with revenue and spend from the same month. Agency and tool invoices are assigned to the month they relate to, not the month they were paid. Strip everything but media out of the denominator and you get blended ROAS: a higher number for the same business.
Example calculation
Worked example: an e-commerce store, one calendar month.
| Total revenue net of VAT, after returns | €400,000 |
| Media spend across all platforms | €60,000 |
| Agency €9,000 + tools €2,000 + creative production €4,000 | €15,000 |
| Total marketing spend | €75,000 |
| MER = 400,000 / 75,000 | 5.33 |
| Blended ROAS on media only = 400,000 / 60,000 | 6.67 |
Same month, two numbers. The gap between 5.33 and 6.67 is nothing but €15,000 of non-media costs that blended ROAS does not see. When results are reviewed against the books, MER is the number that applies.
Relation to margin and reading the result
MER on its own does not say whether the company makes money. Contribution margin decides that: revenue minus cost of goods, shipping, packaging and payment fees, before marketing. The zero line is break-even MER = 1 / contribution margin. At a 25% margin that is 4.0: every euro put into marketing has to bring in four euros of revenue for the margin to cover exactly what marketing cost. The store in the example has an MER of 5.33, so it is above the line. Check: 400,000 × 25% = €100,000 of contribution margin, minus €75,000 of marketing = €25,000 left for fixed costs and profit. If the company wanted 10% of revenue left after marketing, the target MER is 1 / (0.25 minus 0.10) = 6.67, which at the same spend means €500,000 of revenue. MER is therefore always read together with margin and as a trend over time, never as a standalone number.
What MER is for
MER is the checksum above platform reports. When every channel reports growth while MER falls, the channels are crediting each other's conversions and the real efficiency of marketing is declining. A worked example: a company with 10 million in revenue and 1 million of marketing spend has an MER of 10. Double the spend and grow revenue to 13 million, and MER drops to 6.5: the growth is real, but every additional unit of spend now brings less. Tracking MER over time shows where diminishing returns from scaling begin.
From our own practice
We use MER as the top layer of reporting above campaign metrics across EUR 52 million of managed spend: campaigns are steered by POAS and target values, but the monthly review with the client stands on MER, because it matches the books and cannot be broken by a measurement change. A typical benefit: when credited conversions drop after consent or measurement changes, MER shows whether the business fell or just the measurement. Without it, such situations produce unnecessary panic.
Common mistakes
- Steering individual campaigns by MER. It is an aggregate. Campaign decisions need campaign metrics.
- Comparing MER between companies. It depends on margin, brand share and growth stage. Only your own trend is meaningful.
- Leaving costs out. If agencies, tools and production are missing from the denominator, the number lies.
Related terms
See also POAS, ROAS, incrementality, marketing mix modeling and CAC.
Frequently asked questions
What is a healthy MER?
It depends on margin: at a 30 percent contribution margin, an MER of 3.33 is the zero line. A healthy value is therefore individual. The trend and the relation to margin matter more.
MER or blended ROAS?
Same principle. Blended ROAS usually counts media spend only, MER all marketing costs. What matters is picking one definition and keeping it.
How often should MER be tracked?
Monthly, weekly in season. A daily MER is noise, because revenue and spend are not synchronous.
How we can help
We build reporting from campaigns up to business numbers as part of our Performance marketing agency service.