What is marketing efficiency ratio (MER)?
Marketing efficiency ratio (MER) is total revenue divided by total marketing spend, across every channel. It uses your store's own numbers, so no ad platform's attribution sits in between. It answers a whole-business question: how much revenue comes in for each dollar spent on marketing.
The formula
Use the same dates for both numbers. Revenue includes sales no ad touched, so MER is a whole-business number rather than a verdict on one campaign.
Worked example
Revenue is 4.00× marketing spend, so marketing costs 25 cents of every dollar of revenue.
Using it on Meta ads
Watch MER beside the ROAS Meta reports. If Meta's ROAS rises while MER falls, the platform may be crediting sales that would have happened anyway.
Set MER against your break-even ROAS to see whether the business makes money on its marketing as a whole, and against CAC to see what new customers cost.
Questions
ROAS divides the revenue one platform credits to its ads by that platform's spend. MER divides all revenue by all marketing spend, so it needs no attribution and counts no sale twice.
Every paid channel at least: Meta, Google, TikTok and the rest. Some teams add agency fees, creators and tools. Whatever you choose, keep it the same from month to month so the numbers compare.
Each platform counts the sales it believes it caused, and two platforms can both claim the same sale. MER is built from your store's own revenue, so it is a check on what the platforms report.
