In many meetings the single word “ROAS” is said while everyone at the table means a different number. The result is a long argument about an undefined figure.
Platform ROAS answers one question: how much revenue did this ad drive according to the platform’s own attribution? It is an ad metric, shaped by the attribution window, duplicates, orders the platform never saw, and cancellations after the click.
MER (Marketing Efficiency Ratio) answers the business question: total revenue over total marketing spend in the same period. No attribution, no window, no platform. One number telling you how efficiently the whole system turns spend into revenue.
Profit ROAS answers the profitability question: after cost of goods, variable fees, confirmation, and delivery, how much actual contribution did each pound of spend return? This is the number that decides whether you can scale.
The working rule:
- Platform ROAS to optimize ads and creative inside the platform.
- MER to monitor system health weekly and monthly.
- Break-even and Profit ROAS for the scale-or-stop decision.
If the three move in different directions it is not a contradiction. It means something between ad and revenue still needs a definition: a window, a successful-order definition, or a measurement source.
Bottom line: before saying “ROAS is good”, say which ROAS, over which period, from which source.