What is MER (Marketing Efficiency Ratio)?

MER (marketing efficiency ratio) is total business revenue divided by total marketing spend across all channels. It is the blended, whole-business answer to "is our marketing paying off" — sometimes called blended ROAS.

Formula: MER = Total Revenue / Total Marketing Spend

The mechanics

Platform-reported ROAS has become less trustworthy as tracking loss and cross-channel influence blur attribution, so MER steps back and measures the whole system: every dollar of revenue against every dollar of marketing. Its strength is that it cannot be gamed by attribution settings; its weakness is that it cannot tell you which channel or ad deserves credit. Most operators use MER as the guardrail for total spend and in-platform metrics for creative-level decisions.

Signals that matter

• Good: MER holding steady or improving while total spend scales up
• Bad: platform ROAS looks great while MER declines — channels are claiming credit for the same sales
• Bad: MER propped up by returning-customer revenue while new-customer acquisition quietly stalls

Putting it to work

Because MER moves slowly and blends everything, the day-to-day lever underneath it is still creative: better ads lift efficiency everywhere at once. A steady cadence of fresh UGC-style tests — easy to produce in batches inside Claude with Polaris — is how you defend MER as spend grows. See the full ecommerce ads glossary, or put it into practice with the Polaris AI UGC ad generator.