MER Calculator
Total revenue divided by total ad spend. One number, no attribution, nothing to argue about — and the target your margin actually requires.
Everything you collected, including organic and repeat.
Share of the order left after every cost except advertising.
MER
4.00x
- Ad cost as a share of revenue
- 25.0%
- Target MER
- 3.13x
At 4.00x you are clearing the 3.13x needed for a 15% net margin.
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What MER measures
Marketing efficiency ratio is total revenue divided by total ad spend, across every channel, for a period.
MER = total revenue ÷ total ad spend
What makes it useful is what it refuses to do. It does not ask which campaign caused which sale. It takes the money that arrived and the money that went out, and divides. No pixel, no attribution window, no two platforms claiming the same order.
That bluntness is the point. Platform ROAS answers “did this campaign work?” and gets it wrong in predictable directions. MER answers “is the business making money on advertising?” and cannot be gamed, because the numerator is your bank balance.
Getting the inputs right
- Total revenue
- Everything you collected in the period — paid, organic, email, repeat, all of it. The temptation is to use only “attributable” revenue, which quietly turns MER back into ROAS and throws away the reason to use it.
- Total ad spend
- Every channel, including the ones you do not think of as performance: retargeting, influencer fees, affiliate commissions. If it is spend intended to produce sales, it belongs here.
- Contribution margin
- Used only to compute your target MER. Blend it across the products you actually sell rather than using your best SKU, or the target will be optimistic in exactly the way that hurts.
- Target net margin
- What you want to keep after everything. The calculator returns the MER required to get there, which is often uncomfortably higher than where you are.
A worked example
A store doing $50,000 in a month on $12,500 of total ad spend. MER is 4.00x, meaning advertising costs 25% of revenue.
With a blended contribution margin of 47% and a 15% net margin target, the required MER is 1 ÷ (0.47 − 0.15) = 3.13x. At 4.00x this account is clearing its target with room to spare, and the honest conclusion is that it could probably afford to spend more.
Move the target to 30% net and the required MER becomes 5.88x — well above where the account sits. Same business, same performance; the target simply is not compatible with a 47% contribution margin at this spend level. That is a pricing conversation, not a media-buying one.
MER versus ROAS, and when each lies
MER is always lower than the sum of your platform ROAS figures, and the gap is the interesting part. Platforms over-claim: two of them will happily take credit for the same order. MER cannot, because revenue is counted once.
But MER has a real weakness, and it is worth naming. It cannot tell you which channel to cut. A 4.00x account with one channel at 8x and another at 1.2x looks identical to an account with everything at 4x. MER tells you whether the machine is working; it says nothing about which part.
The practical pairing is to steer with MER and diagnose with channel-level data — while remembering the channel data is over-attributed. The blended ROAS calculator quantifies exactly how much.
Questions
- What is a good MER?
- It depends entirely on your contribution margin, which is why the calculator derives a target rather than quoting an industry figure. A 60% margin business is fine at 2.5x; a 30% margin business at 2.5x is losing money. Any benchmark quoted without a margin attached is describing someone else's cost structure.
- What is the difference between MER and blended ROAS?
- In most usage, nothing — both are total revenue over total ad spend. Where people distinguish them, blended ROAS is used for a campaign-level roll-up while MER is used at account level over a period. The important difference is not between these two terms but between either of them and platform-reported ROAS.
- What is aMER?
- Acquisition MER: new-customer revenue divided by total ad spend. It is a stricter test, because it removes repeat purchases that would have happened anyway. If MER looks healthy but aMER is weak, your advertising is largely paying to reach people who were already coming back.
- Should organic revenue be in the numerator?
- Yes. That is the whole point. Advertising creates demand that later arrives through search, direct and email, and excluding it means understating what your spend produced. If you want the stricter view, use aMER rather than stripping organic out of MER.
- What period should I measure over?
- Long enough to cover your purchase consideration cycle, usually a month. Weekly MER is noisy for anything with a delay between first touch and purchase, and daily MER mostly measures which day your ads happened to run.
Sources and last update
Last verified 2026-08-22.
Figures here are planning estimates. Duty applies per 10-digit HTS code and platform fees change without much notice — check your own broker and your own seller account before committing spend. Full workings on the methodology page.