Glossary - Acquisition and attribution
MER (marketing efficiency ratio)
MER (marketing efficiency ratio) is total store revenue divided by total marketing spend for a period, across every channel, with no attribution model involved. Ecommerce operators use MER as a whole-business check on marketing efficiency that platform-reported attribution cannot inflate, tracked against a margin-based floor rather than a universal benchmark.
| Total revenue | All store revenue for the period - every order, every channel, new and returning customers. |
| Total marketing spend | Everything spent on marketing in the period: ad spend across platforms plus agency fees, affiliate commissions and other variable marketing costs. |
Worked example
A 5.0 MER here leaves 20% of revenue as contribution after marketing. The same 5.0 at a 15% pre-marketing margin would lose money - the ratio means nothing without the margin next to it.
What is a good MER?
There is no universal good MER. The break-even MER is 1 divided by contribution margin before marketing - the same arithmetic as break-even ROAS, applied to the whole account - so a 5.0 can be comfortable at a 40% margin and underwater at 15%.
Beyond margin structure, the right MER depends on posture: heavier prospecting spend lowers MER today in exchange for repeat revenue later, and a rising MER can simply mean you stopped investing in growth. Work out your own floor and target with the free target MER calculator.
MER vs related metrics
| Metric | What it measures | How it differs from MER |
|---|---|---|
| ROAS | Attributed revenue ÷ ad spend for one campaign or channel. | Campaign-level and attribution-dependent; MER is account-level and attribution-free. |
| POAS | Contribution margin from attributed orders ÷ ad spend. | Margin-aware but still attributed; MER stays on revenue and the whole account. |
| Blended CAC | Total sales and marketing spend ÷ all new customers. | The same attribution-free logic, pricing customers instead of revenue. |
Common mistakes
- Undercounting the spend side. Agency fees, affiliate commissions and influencer costs are marketing spend; leaving them out flatters MER.
- Reading MER without margin context. Whether 5.0 is good depends entirely on your pre-marketing contribution margin.
- Celebrating a rising MER that came from cutting prospecting - efficiency up now, growth starved later.
- Using MER to judge a single campaign or channel. It is blended by construction and cannot allocate credit.
- Comparing MER across periods with different promo cadence or new-versus-returning mix as if conditions were equal.
FAQ
Yes, in common usage: both names describe total revenue divided by total marketing spend for a period. The point of either name is that no attribution model is involved.
1 divided by your contribution margin before marketing. At a 40% margin, marketing spend consumes the entire margin pool once MER falls to 2.5; anything above that leaves contribution behind.
Because MER cannot be inflated by attribution overlap: it compares money in the bank with money spent. It catches the drift when every platform's ROAS looks fine but the blended picture is getting worse.
Related
In Blufire, S6 Marketing & Channels tracks CM1-MER per channel - the same ratio computed on contribution margin instead of revenue, channel by channel.
Updated July 2026