A metric that escapes attribution
A platform's ROAS rests on the conversions it attributes to itself. MER attributes nothing: it divides the revenue actually collected by total spend. No sale is counted twice, and no sale lost by tracking disappears from it.
That is what makes it a safeguard. If every platform reports rising ROAS while MER stays flat, the extra sales only exist in the reports. MER settles the debates that attribution cannot.
It is also known as blended or consolidated ROAS. Some teams track its inverse: the share of revenue spent on marketing.
What MER does not tell you
MER measures everything, so it points to nothing: it does not tell you which channel is working. An increase can come from an effective campaign just as well as from a favorable season, a price increase, or word of mouth that cost nothing.
It also includes the revenue that would have come in without any advertising: loyal customers, organic traffic, established brand awareness. An established brand shows a high MER even with mediocre campaigns; a young brand, a low MER even with good campaigns.
To isolate acquisition, a useful variant keeps only the revenue from new customers. It answers a more precise question: what growing the customer base really costs.
Set MER at the top, steer ROAS below
The target MER follows from the economics of the business. With a 50% gross margin and the goal of keeping 20% of revenue after marketing, marketing spend can reach 30% of revenue, which gives a floor MER of about 3.3.
Platform ROAS is then used to split the budget across channels and campaigns, knowing that it is biased. MER checks that the sum of those decisions holds up.
It is read over periods long enough to smooth out the lag between spend and sales, and compared year on year, season for season. Over a single week, it mostly reacts to the calendar.
Frequently asked questions
How do you calculate MER?
Divide total revenue for the period by total marketing spend for the same period. €200,000 of revenue for €40,000 of spend gives an MER of 5.
What is the difference between MER and ROAS?
ROAS credits a campaign with the sales attributed to it. MER compares all revenue with all spend, with no attribution. The first is for choosing between campaigns, the second for checking that the whole is profitable.
Which costs should go into MER?
At a minimum, all ad spend across every platform. Some teams add tools, agencies, and partnerships; what matters is keeping the same definition from one period to the next.
What is a good MER?
One that leaves enough margin after marketing to cover fixed costs and reach the profit you are aiming for. It follows from your gross margin, not from an industry average.