Why it matters
Every ad platform marks its own homework. Meta, Google and an affiliate network can each claim credit for the same order, so their ROAS figures can add up to more revenue than you actually made. MER sidesteps the argument by using the revenue in your store and the spend on your invoices. If MER is healthy, your marketing is paying off as a whole, whatever each dashboard says.
How to calculate it
Divide total revenue for a period by total marketing spend for the same period. Include all paid media, influencer fees and — for a strict view — agency and tool costs. Decide whether revenue is before or after returns and GST, and keep it the same every month. The ROAS calculator works for MER too: just enter totals.
Worked example
Example: one month for a D2C skincare brand.
| Source | Spend | Revenue the platform claims |
|---|---|---|
| Meta | ₹2,50,000 | ₹8,00,000 (ROAS 3.2) |
| ₹1,00,000 | ₹4,50,000 (ROAS 4.5) | |
| Influencers | ₹50,000 | — |
| Total | ₹4,00,000 | Store revenue: ₹12,00,000 |
Meta and Google together claim ₹12,50,000 — more than the store's entire revenue, which also includes organic and repeat orders. The MER of 3.0 is what actually happened.
MER vs platform ROAS
Platform ROAS works at the level of a campaign, ad set or ad, so it's the right tool for choosing between ads inside Meta. But it relies on attribution, so it can double-count and over-credit. MER can't tell you which channel caused what, but it can't be inflated either. Use both: platform ROAS to allocate within Meta, MER to decide whether spending more is growing the business.
What's a good MER?
Work out your break-even MER the same way as break-even ROAS: 1 ÷ your average contribution margin %. If the average order keeps 40% after product and fulfilment costs, break-even MER is 2.5. Your target sits above that by enough to cover fixed costs and profit.
How to use it
- Track MER weekly alongside total spend. If you raise Meta budgets by 30% and total revenue barely moves, MER falls — the extra spend is mostly claiming sales you'd have made anyway, a question for incrementality testing.
- Set the total budget with MER, then allocate it with platform ROAS.
- When scaling, watch MER as well as in-platform ROAS — see how to scale Meta ads without killing ROAS.
Common mistakes
- Comparing MER across months with big swings in organic demand, such as festive seasons or press coverage.
- Leaving out spend like influencer fees, which flatters MER.
- Using MER to judge individual ads — it's too blunt for that.
Frequently asked questions
What is the difference between MER and ROAS?
ROAS measures the revenue a platform attributes to a campaign or ad, divided by that spend. MER divides your total revenue by your total marketing spend across every channel. Because MER doesn't depend on attribution, platforms double-counting the same sale can't inflate it.
What is a good MER for an e-commerce brand?
It depends on your margins and fixed costs. Your break-even MER is 1 divided by your average contribution margin percentage — 2.5 at a 40% margin, for example. A good MER sits far enough above that to cover overheads and leave profit.
Is MER the same as blended ROAS?
Mostly, yes: both divide total revenue by total spend, and many people use the terms interchangeably. Some teams count only paid media in blended ROAS, while MER may also include agency fees, influencer costs and tools. Define which costs you include and keep it consistent.
