ROAS vs MER
Short answer: ROAS measures the return on a single channel or campaign, while MER (marketing efficiency ratio) measures total revenue against total marketing spend. Use ROAS to optimize channels and MER to judge whether the whole machine is profitable.
If you have ever had every channel report a winning ROAS while the bank account quietly shrank, you have met the reason MER exists. The two metrics answer different questions, and the trouble starts when you use one to answer the other.
What each one measures
ROAS = revenue from a channel ÷ spend on that channel. It is great for deciding where the next dollar goes. MER = total revenue ÷ total marketing spend. It does not care about attribution, it just asks whether all your marketing, together, is paying off.
The double-counting problem
Modern platforms over-claim. Google, Meta, and TikTok can each take credit for the same sale, so if you add up their reported ROAS you get a number that never shows up in revenue. MER cuts through this because it uses one honest figure: the money that actually came in. When channel ROAS looks great but MER is weak, you are usually double-counting conversions.
You can compute both side by side in the ROAS / MER calculator.
How to use them together
- Watch MER as your north star for overall profitability.
- Use ROAS to shift budget between channels at the margin.
- When the two disagree, trust MER and audit your attribution.
A worked example: when ROAS lies and MER tells the truth
A store spends $10,000 across three channels in a month and the platforms report these returns:
| Channel | Spend | Reported revenue | Reported ROAS |
|---|---|---|---|
| $4,000 | $16,000 | 4.0× | |
| Meta | $4,000 | $14,000 | 3.5× |
| TikTok | $2,000 | $6,000 | 3.0× |
| Sum of platforms | $10,000 | $36,000 | 3.6× |
Every channel looks profitable, and the platforms together claim $36,000. But the store's actual revenue that month, from its own checkout, was $24,000. MER = $24,000 ÷ $10,000 = 2.4×, not 3.6×. The $12,000 gap is the same buyers counted two or three times as different platforms each claimed the sale. If your break-even ROAS is 2.5× (a 40% margin business), the platform numbers say "scale up" while MER says "you are slightly underwater." MER is the one tied to the bank account, so MER wins.
FAQ
Which is more important?
MER for the business, ROAS for the channel. You need both.
What is a good MER?
Like ROAS, it depends on margin. Compare it to your break-even ROAS, see what is ROAS.