MER (media efficiency ratio) is total revenue divided by total marketing spend, across every channel — not just the ones an ad platform can attribute a click to. Enter both numbers for a period below.
MER calculator
"Total marketing spend" means every channel — paid social, search, affiliates, influencers, email tools, the lot — not just what one ad platform reports.
ROAS is usually calculated per platform, using that platform's own claimed attribution — a click or view it tracked, within its own attribution window. MER skips attribution entirely: total revenue from your store's own numbers, divided by total spend from your own books. Nothing to attribute, so nothing for a platform to over-claim.
| ROAS | MER | |
|---|---|---|
| Revenue counted | Only what the platform attributes to itself | All store revenue, every channel and no-click sales included |
| Spend counted | One platform's spend | Every marketing channel's spend combined |
| Double-counting risk | High — two platforms can both claim the same sale | None — each sale is counted once, in total revenue |
| Granularity | Can isolate one campaign or platform | Only a whole-business number, not per-campaign |
Neither number is "more correct" — they answer different questions. ROAS (imperfectly) tells you whether a specific campaign is working. MER tells you whether the whole marketing budget is working, whatever mix of attributed and unattributed sales it produced.
Someone sees your product mentioned in a Reddit thread, doesn't click anything, and buys two weeks later by typing your brand name into Google or going straight to your site. No ad platform attributes that sale to itself, because there was no ad click to attribute. It still shows up in total revenue, which is why MER is often noticeably higher than a blended sum of platform-reported ROAS.
That gap is genuinely useful information — it's roughly the size of your unattributed, word-of-mouth and organic demand. You can't turn it into an exact dollar figure the way you can a tracked ad click, but you can at least see the conversation behind it: Mentionfront tracks brand and product mentions across TikTok, Instagram, X, Reddit, YouTube and Facebook, so when MER and blended ROAS diverge, there's somewhere to go look for why.
Same period, two numbers
Example workspace · last 30 days
The mechanical reason platform ROAS and store revenue never line up, put plainly in a public r/ecommerce post about high-ticket products:
Meta uses a 7-day click and 1-day view attribution. It tracks when someone interacts with an ad and converts later. Shopify, on the other hand, records the order exactly when it's created… FB will claim that sale, but Shopify's "Last Click" logic might give it to the YouTube link or just mark it as direct.
MER sidesteps the argument rather than settling it. It doesn't care which platform earned the credit, because it only uses two numbers neither platform controls: what you actually spent, and what your store actually took. That's also its limit — when MER moves, it won't tell you which channel moved it.