What is MER?
Marketing efficiency ratio, total revenue divided by total advertising spend across every channel.
MER = Total Revenue / Total Ad Spend
A worked example
Your business does Rs 24,00,000 in revenue this month and spends Rs 6,00,000 across Google, Meta and Amazon combined. Your MER is 4.0. Meanwhile Meta claims a 3.2 ROAS and Google claims 4.5, which together account for more revenue than the business actually made.
Why it matters
MER exists because platform-reported ROAS stopped being trustworthy. Every channel claims conversions within its own attribution window, nobody deducts what the others counted, and the totals routinely exceed real revenue. MER sidesteps the argument entirely by using two numbers that cannot be inflated: money that arrived in your account, and money that left it.
This makes it the right metric for deciding total budget, even though it cannot tell you how to split that budget. If MER is above the level your margin requires, spending more is usually right. If it is below, the problem is the whole marketing system rather than one campaign.
It is particularly useful for brands running several channels at once, where the interaction between them is invisible to each platform. Meta builds awareness that Google captures as branded search. Both claim it. MER counts it once.
The nuance most people miss
MER measures the whole business, which means anything affecting revenue moves it, including things that have nothing to do with marketing. A large wholesale order, a seasonal spike or a pricing change will shift MER without any campaign performing differently. Watch it as a trend over months rather than reading week to week, and keep channel-level metrics alongside it for diagnosis. MER tells you whether to spend more or less overall; it will never tell you which campaign to pause.
Common mistakes
- Using MER to make campaign-level decisions, which it cannot support
- Comparing MER month to month in a seasonal business without accounting for the season
- Including revenue from channels that advertising does not touch, such as wholesale, without noting it
- Abandoning channel metrics entirely, which leaves you no way to diagnose why MER moved