In one sentence
Marketing efficiency ratio is your total revenue divided by your total marketing spend across every channel, and it shows whether your marketing as a whole is paying off, even when tracking can't credit each sale.
How to calculate MER
MER = total revenue divided by total marketing spend, for the same period.
If your store made $120,000 last month and you spent $30,000 on all marketing, your MER is 4. Every marketing dollar sat alongside $4 of revenue.
Include everything: ads on every platform, influencers, affiliates, email and SMS tools, and agency fees if you count them as marketing.
MER vs. ROAS
Use ROAS to tune campaigns. Use MER to check the platforms aren't all claiming the same sale.
Why MER matters for ecommerce brands
Ad platforms each report their own wins, and the totals often add up to more sales than you made. MER ignores the claims and asks one question: did spend and revenue move together?
It also captures channels that are hard to track, like word of mouth and AI answers that send shoppers to your store without a click you can attribute.
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