What is MER?
MER, or marketing efficiency ratio, is your total store revenue divided by your total marketing spend across every channel, so it measures the whole business instead of one campaign.
Formula
MER = total store revenue ÷ total marketing spend
Worked example, not a result
Working out MER for a month
Say a store takes 95,000 in revenue over a month from every source combined, including organic search, direct visits, email and paid clicks. Over the same month it spends 25,000 on marketing: 15,000 on search and shopping, 7,000 on social ads, and 3,000 on agency fees, email software and creative production.
MER is 95,000 divided by 25,000, which is 3.8. The whole store returned three point eight units of revenue for every unit put into marketing, no matter which channel gets the credit.
The useful part is what happens next month. If spend rises to 31,000 and revenue rises to 108,000, MER falls to about 3.5 even though revenue grew. That is the honest signal that the extra spend bought less than the spend before it, which no single platform report would have told you.
These are invented figures used to show the calculation, not results from any store.
Why it matters
MER answers the question every owner actually asks, which is whether the money going into marketing is making the business bigger. Platform reports cannot answer that, because each one counts the sales it touched and none of them see the whole picture.
It sits across all four levers at once. Rising visitor numbers push revenue up and MER with it. A better conversion rate or a higher average order means the same clicks turn into more revenue, so MER improves with no change in spend. Strong repeat purchases are the biggest lift of all, because returning customers add revenue to the top of the ratio while costing almost nothing at the bottom.
For decisions, MER is the number to watch when you increase budget. Track it weekly against total revenue and you can see the point where extra spend stops carrying its weight, which is the moment to fix a lever instead of buying more clicks.
Common mistakes
- Leaving costs out of the bottom half. If retainers, software, creative and influencer payments are excluded, MER looks better than the business is and every budget decision is made on a soft number.
- Judging MER over a few days. Revenue arrives on a different rhythm than spend, especially with email and repeat orders, so a short window swings wildly and tells you nothing.
- Using MER as the only number. It cannot tell you which channel is working, so pair it with per channel reporting rather than replacing it.
- Expecting MER to hold steady while you grow. Spending more to reach colder audiences almost always lowers it, and the real question is whether the lower ratio still leaves enough contribution.
Related terms and answers
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