Add up the revenue Meta says it drove last month. Add Google's. Add TikTok's.
Now compare the total to what actually landed in your bank.
The platforms almost always claim more. Every channel takes credit for the same sale.
MER is the number that can't play that game.
The short version
MER, or marketing efficiency ratio, is your total revenue divided by your total marketing spend.
MER = total revenue ÷ total marketing spend
Say your store made $200,000 last month and you spent $50,000 on marketing across every channel. Your MER is 4.0.
You'll also hear it called blended ROAS. Same thing.
One warning: some tools flip it and show spend as a percentage of revenue. The same month would read 25%. Check which way round your tool does it before you compare numbers.
MER vs ROAS
ROAS is one channel's claimed revenue divided by that channel's spend. The revenue number comes from the platform, using the platform's own rules about what it caused.
MER is all your revenue divided by all your spend. The revenue number comes from your store.
Both are useful. They answer different questions.
ROAS tells you which ads to keep. MER tells you whether the business is working.
The bank statement test
I have one rule for any marketing number that goes in a report. I call it the bank statement test: would your bank statement agree with it?
Platform ROAS often fails. Meta counts a sale if someone saw your ad and bought within a set window. Google counts the same sale if they also clicked a search ad. Add the channels together and you can "earn" more than you sold.
MER passes. Revenue is revenue. Spend is spend. Nothing gets counted twice.
Decide what counts as spend
Ad spend on every channel always goes in. After that, you choose: creator fees, agency fees, design costs, software.
There's no single right answer. A narrow definition (ads only) is easier to compare month to month. A wide one (everything you spend to get sales) is more honest about cost.
Pick a definition once and never change it. A consistent MER beats a perfect one.
Break-even MER
MER works the same way as ROAS. Your margin sets the floor.
Break-even MER = 1 ÷ contribution margin
If 40% of each order is left after product, shipping and fees, your break-even MER is 2.5. Below 2.5, your marketing costs more than your orders leave behind. Above it, marketing is paying for itself. The break-even calculator does the math for you.
You'll find published MER "benchmarks" too. They vary wildly from one source to the next, because margins and repeat rates vary wildly. Your break-even tells you more than any of them.
aMER: the stricter version
MER has one weakness. Revenue from returning customers counts too, even if your ads didn't bring them back.
As a brand grows its repeat business, MER can look better while new customer growth stalls.
The fix is acquisition MER:
aMER = revenue from new customers ÷ total marketing spend
If MER is steady but aMER is falling, your spend is taking credit for customers you already had.
How I use MER
1. Set a target from the margin. Break-even MER plus the profit you want. That's the line for the whole business.
2. Watch weekly, not daily. Daily MER jumps around with email sends and paydays. Weekly shows the trend.
3. Scale until the extra spend stops paying. When you raise the budget, look at what the extra money brought in, not the average.
Marginal MER = extra revenue ÷ extra spend
If you add $10,000 of spend and revenue rises $30,000, the extra spend ran at a marginal MER of 3.0. When that number falls to break-even, stop scaling.
Here's a made-up example of a brand with a 40% margin, so a break-even MER of 2.5, scaling week by week:
| Week | Spend | Revenue | MER | Marginal MER |
|---|---|---|---|---|
| 1 | $20,000 | $100,000 | 5.0 | - |
| 2 | $30,000 | $135,000 | 4.5 | 3.5 |
| 3 | $40,000 | $160,000 | 4.0 | 2.5 |
| 4 | $50,000 | $175,000 | 3.5 | 1.5 |
Look at the MER column alone and week 4 still looks healthy. 3.5 is well above break-even.
The marginal column tells the truth. The last $10,000 brought in only $15,000. At a 40% margin, that extra spend lost $4,000. Week 3 was the place to stop.
Average MER tells you where you are. Marginal MER tells you where the next dollar goes.
4. Use both numbers, for different jobs. MER sets the total budget. Platform ROAS decides which campaigns and ads inside it get the money.
Where MER misleads
- Promotions. A big sale spikes revenue and MER, while the discount quietly eats the margin.
- Seasonality. November MER and February MER aren't the same game. Compare against the same period last year.
- Lag. Spend today can turn into sales next week, especially on higher-priced products.
- Organic and email. Revenue you'd have made anyway still lands in the total. That's what aMER is for.
None of these break MER. They just mean you read the trend, not one week in isolation.
It also helps to make the platforms' numbers more honest. Better tracking through the Conversions API won't change your MER, but it shrinks the gap between what Meta claims and what you see.
Pool rule 009Report decisions, not dashboards.
Quick answers
What does MER stand for in marketing? Marketing efficiency ratio: total revenue divided by total marketing spend.
Is MER the same as blended ROAS? Yes. Both divide all revenue by all marketing spend.
What is a good MER? One comfortably above your break-even MER, which is 1 ÷ contribution margin. At a 40% margin that's anything well above 2.5.
What's the difference between MER and CAC? MER divides revenue by spend. CAC divides spend by the number of new customers. MER tells you about efficiency, CAC about the price of a customer.
Does MER work for lead generation? Yes, if you use revenue from closed deals. Expect more lag between spend and revenue than in ecommerce.
The one-line version
ROAS picks the ads. MER tells you whether the ads are paying the bills.