Definition
Marketing efficiency ratio (MER) is total store revenue for a period divided by total marketing spend for the same period, across every channel at once. It answers one question: for each dollar the store spent on marketing, how many dollars of revenue came in. Unlike ROAS, which is reported per platform using that platform's own attribution, MER uses the order total from the store and the spend total from the finance side, so no channel can claim a sale that another channel also claimed.
Formula
MER = Total revenue ÷ Total marketing spend
- Total revenue
- All store revenue for the period from the platform's order data, usually net of discounts and before or after returns, stated consistently
- Total marketing spend
- Every marketing cost in the period: ad spend on all platforms, agency and tool fees, affiliate and influencer payments
A month, worked with the reader's own shape of numbers
- Store revenue for the month
- $240,000
- Google Ads and Shopping spend
- $28,000
- Meta spend
- $19,000
- Email platform, feed tool and agency fees
- $7,000
- Total marketing spend
- $54,000
- MER
- 240,000 ÷ 54,000 = 4.4
Illustrative figures. A MER of 4.4 means every marketing dollar was matched by 4.4 dollars of revenue. Whether that is healthy depends on the store's gross margin and what MER it needs to break even, which is why the number is read next to contribution margin rather than on its own.
Why it matters
MER matters because platform-reported ROAS drifts away from reality as a store adds channels. Google, Meta and an affiliate network can each attribute the same order to themselves, so the sum of their reported revenue exceeds what the store actually banked. MER sidesteps that argument by starting from the order total. It moves slowly and it does not tell you which channel to cut, but it tells you honestly whether the whole marketing budget is paying for itself, and it is the first number a finance lead will trust. Tracked weekly or monthly, it also reveals when growth in spend has stopped producing growth in revenue, which platform dashboards tend to hide.
Where it goes wrong
- Comparing MER between stores or industries: a store with a high gross margin can grow profitably at a MER that would sink a low-margin store, so the only useful benchmark is the store's own break-even MER
- Leaving costs out of the denominator: agency fees, feed tools, influencer product and affiliate commissions are marketing spend, and omitting them flatters the ratio
- Reading a rising MER as success while cutting spend: MER often rises when a store stops acquiring new customers, because brand and repeat revenue keep coming in without spend, so it must be read next to new customer counts
- Mixing periods: revenue from orders placed this month against spend that ran last month, or the reverse, makes the ratio swing for reasons that have nothing to do with efficiency
Questions about MER
What is the difference between MER and ROAS?
ROAS is revenue attributed to one platform divided by spend on that platform, using that platform's attribution model. MER is all store revenue divided by all marketing spend. ROAS tells you how a channel looks through its own reporting; MER tells you whether the whole budget is paying off according to the store's order data.
What is a good MER for an ecommerce store?
There is no universal number. The useful reference is the store's own break-even MER, which comes from gross margin: a store keeping 60 cents of every revenue dollar after product and fulfilment costs breaks even at a MER of about 1.7, while a store keeping 30 cents needs about 3.3 just to stand still. Anything above the break-even figure is margin; how far above depends on the growth the owner wants to fund.
How often should MER be tracked?
Weekly for direction and monthly for decisions. Daily MER swings with order timing and spend pacing and is rarely worth reacting to. A monthly MER read next to new customer count and contribution margin is enough to decide whether to raise, hold or cut the budget.