Blended ROAS, often measured as MER (marketing efficiency ratio), is total revenue divided by total marketing spend across all channels, rather than per-platform attributed revenue. It is the number that cannot be inflated by attribution.
Why blended beats platform ROAS
Every platform claims credit for the same sales, so summing their reported ROAS overstates reality. Blended ROAS sidesteps this: total revenue over total spend, no attribution required. MER is the same idea expressed as a ratio of revenue to marketing cost. It is the board-level truth that platform dashboards cannot flatter.
How to use it
Use blended ROAS or MER as the top-line health metric and platform ROAS only as a directional signal for optimization. When platform-reported ROAS rises but blended does not, the platforms are re-claiming existing sales, not creating new ones. It complements a single source of truth in the attribution stack.