MER: the number, and what it hides
Total revenue divided by total ad spend, ignoring attribution entirely.
Why mer matters
It cannot be gamed by attribution settings, because it does not use them. When platform ROAS and MER disagree, MER is usually the one the finance team believes.
What this looks like with real numbers
The business did $210,000 of revenue on $60,000 of total ad spend, so MER is 3.5. If platform-reported ROAS across channels implies $310,000 of attributed revenue, the gap is double-counting between platforms, and MER is the number to plan against.
What it does not tell you
It cannot tell you which channel or which ad did the work. It is a business-level health check, not a decision-making tool at ad level.
The mistake people actually make
Using MER to judge an individual ad. It is a business-level check and cannot tell you which creative did anything.
Questions, answered.
How do you calculate mer?
Total business revenue ÷ total ad spend. Total revenue divided by total ad spend, ignoring attribution entirely.
What goes wrong with mer?
Using MER to judge an individual ad. It is a business-level check and cannot tell you which creative did anything.
What does mer not tell me?
It cannot tell you which channel or which ad did the work. It is a business-level health check, not a decision-making tool at ad level.
Change the creative, not the dashboard
Total revenue divided by total ad spend, ignoring attribution entirely.