Definition
MER (Marketing Efficiency Ratio) is your total revenue divided by your total marketing spend across every channel. It ignores the platforms' own attribution and shows how efficiently the whole marketing machine is working.
Also called: Marketing Efficiency Ratio, Blended ROAS, aMER, bMERSeveral channels can claim the same purchase.
All 100 purchases in this example are claimed by at least one channel. Adding channel reports counts shared purchases twice. MER uses store revenue and total marketing spend; it does not determine causal lift.
Why MER exists
Because Meta, Google, TikTok and Pinterest each credit themselves with sales, the same order gets counted several times. Add up the platforms' reported revenue and you can hit 130% of your actual revenue. MER solves this by ignoring attribution entirely and looking at the total.
MER = total revenue / total marketing spend. No crediting, no double-counting. Just what came in and what it cost to bring it in.
aMER and bMER
Some distinguish between aMER (only paid channels in the denominator) and bMER (all marketing spend, including agency and tooling costs). The point is the same: measure efficiency at a level where the numbers can't be inflated by any single platform.
MER relates total spend to revenue but does not isolate advertising’s effect. Seasonality, prices, organic demand and repeat purchases also affect it. Use controlled experiments to assess incrementality.
MER as a steering metric
We use MER as the top-line gauge and POAS/contribution margin to steer within it. MER tells you whether the machine as a whole is efficient; POAS tells you where inside the machine the budget should go.
A worked example — and the scaling test
Picture a quarter: Meta reports ROAS 5, Google ROAS 8, email ROAS 20. Impressive on their own. But add up the attributed revenue and it exceeds your actual revenue, because the channels credit themselves for the same orders. MER cuts through the noise: total revenue of €160k divided by total spend of €40k gives a MER of 4.0. No platform can inflate that number.
When increasing budget, monitor MER alongside contribution and acquisition cost. Stable MER does not prove the additional revenue came from advertising. Falling MER does not prove the sales would have happened anyway. That conclusion needs a credible comparison, such as a control group.
One important nuance: MER has to be read alongside CLTV. A brand with strong retention can deliberately run a lower MER in a growth phase, because the customer value is realized over the coming months. MER tells you the efficiency today; CLTV tells you whether a lower MER today is an investment or a leak.
Frequently asked questions
What's the difference between MER and ROAS?
ROAS is often a platform's own attributed revenue for one channel. MER is your total revenue against your total marketing spend — with no attribution. MER can't be inflated by the platforms and is therefore a more honest measure of efficiency.
What is a good MER?
It depends on margin and the share of repeat purchases. A brand with strong retention can drive growth at a lower MER, because the customer's value is realized over time. So MER should always be read alongside CLTV and contribution margin.
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Nicklas Segatz Mortensen
Growth hacker and fractional CMO with 10+ years' experience and hundreds of millions in managed ad spend behind him. Background from larger Danish and international scale-ups, and from the agency world.
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