Set your target MER from your margin, not a benchmark
MER is marketing efficiency ratio: total revenue divided by total marketing spend, across the whole account, no attribution involved. Your breakeven MER is 1 divided by your contribution margin ratio. Your target MER is 1 divided by that ratio minus the profit you want after marketing. At a 40% margin and a 10% profit goal, that is 2.50x and 3.33x.
Revenue minus discounts, landed COGS (cost plus freight-in plus duty), shipping and fulfilment, and payment and platform fees. Not sure? Step it down in the contribution margin calculator and carry the percentage across.
What the account should keep once marketing is paid: contribution margin after marketing, before fixed costs like rent, salaries and software.
Run the whole account at 3.33x or better and every revenue dollar keeps 10% after marketing. Between 2.50x and 3.33x the account is profitable on variable economics but under your goal; below 2.50x it loses money before fixed costs.
Computed at your 40% contribution margin, nothing assumed. 1 ÷ MER is marketing's share of revenue: the higher the profit goal, the less of the margin pool marketing may spend.
Two ratios, two different questions
Per campaign, platform-attributed
Each platform reports conversions inside its own attribution window, and the windows overlap: one buyer who watches a TikTok video, later clicks a Google search ad, then sees a Meta retargeting impression can generate a conversion in all three dashboards for a single real sale.
As documented in The Math: Meta over-reports roughly 26% above third-party analytics on average; Google Ads runs 15% to 20% high under modelled conversions.
Whole account, two totals
Total revenue divided by total marketing spend. No attribution model touches it, so no platform can inflate it and no sale is counted twice.
The trade: it cannot see an individual campaign or channel. That blindness is also its honesty, which is why it works as the account-wide efficiency floor this page computes.
ROAS answers "did this campaign work, by the platform's own telling". MER answers "did the whole account pay for itself".
Two inputs, both already in your ledger
Take a normal month. From revenue, remove discounts, landed COGS (cost plus freight-in plus duty), shipping and fulfilment, and payment and platform fees. The pieces live in your ledger, your supplier and freight invoices and your payment provider statements; or step them down in the contribution margin calculator.
As a share of revenue, before fixed costs. This is what the account should bank once marketing is paid, and it must sit below your margin: profit can only come out of the margin pool.
Breakeven MER is where marketing consumes the whole margin pool. Target MER is the efficiency that funds your profit goal. Both recompute the moment either input moves.
Actual MER is total revenue for the period divided by total marketing spend across every channel for the same period: revenue from your ledger, spend from each ad platform's billing. Totals only, no attribution.
The whole method is two divisions
Marketing spends out of the margin pool, not out of revenue. Give the whole pool to marketing and you get the breakeven floor. Reserve a slice for profit first and the floor rises to your target.
Assumption, stated plainly: profit here means contribution margin after marketing, before fixed costs. Same margin definitions as The Math; the target only exists while the profit goal sits below the margin.
At a 40% contribution margin before marketing, marketing can take at most 40 cents of each revenue dollar before orders start losing money: breakeven MER = 1 ÷ 0.40 = 2.50x.
To keep 10% of revenue as profit after marketing, marketing may only spend 30 cents of each dollar: target MER = 1 ÷ (0.40 − 0.10) = 3.33x.
Check it: at 3.33x, $1.00 of spend brings $3.33 of revenue. 40% of that is $1.33 of margin; take back the $1.00 of spend and $0.33 remains, which is 10% of the revenue.
These are your live inputs from the calculator above, not a canned example. Change a number up there and this paragraph follows.
Three zones, one decision
Platform dashboards each grade their own homework. MER held against your two floors is the one reading the whole account answers to, and it sorts any week into one of three zones.
The account is funding the plan: marketing is paid, the profit goal is banked, and the margin math says current efficiency can carry more volume if you choose to push it.
Variable economics are positive but the profit goal is not being met: the gap between actual and target MER, times revenue, is the contribution being given up. Growth is being paid for out of profit.
Marketing is consuming more than the whole margin pool: each incremental revenue dollar costs more than it contributes, before a single fixed cost is paid.
Honest about what MER cannot see
We lean on MER because it is ungameable: two totals, no attribution, five minutes a week. But it is a blended average, and blends hide things. Here is where it breaks down, and what we do then.
MER is the whole account in one number. A strong channel can mask a bleeding one for months and blended MER will not flinch. When the question is which channel, MER is the wrong instrument.
The target is built on a single blended contribution margin. Promo weeks, mix shifts and freight changes move the real margin under your feet, and the floors move with it. A target computed on last quarter's margin can quietly go stale.
All revenue lands in the numerator, including repeat orders your email list and existing customer base would have produced anyway. A growing repeat base lifts MER without a single ad improving.
Chasing someone else's MER benchmark is the same mistake as chasing a universal ROAS: the floor is set by your margin and your profit goal, nobody else's. That is the whole point of this page.
What we recommend instead, when the blend is not enough: Blufire S6 Marketing & Channels computes CM1-MER and its decomposition per channel from reconciled orders, and S5 shows how attribution model choice shifts channel credit, so you can see which channels earn their MER rather than borrow it.
When to run it, and what triggers action
Same day each week: total revenue ÷ total marketing spend, held against your breakeven and target. Two weeks running under target is the trigger to investigate, starting with which margin input moved.
Margins drift: new COGS, freight changes, discount depth, product mix. Recompute the contribution margin from the closed month and let the floors move before judging the next month against them.
A sitewide discount lowers the margin ratio, which raises both floors. Price the promo period against its own target MER, not the everyday one, before committing spend.
Questions operators ask
MER is marketing efficiency ratio: total revenue divided by total marketing spend for the same period, across the whole account. Some operators call it blended ROAS. Because it is a division of two totals, it needs no pixels, no tracking windows and no attribution model, which is why no platform can inflate it.
ROAS is per campaign and platform-attributed; MER is the whole account and attribution-free. Platform attribution windows overlap, so one real sale can appear as a conversion in several dashboards: Meta over-reports roughly 26% above third-party analytics on average, and Google Ads runs 15% to 20% high under modelled conversions. Read platform ROAS inside a channel, and read MER over the account as the honest total.
There is no universal good MER: the floor is 1 divided by your contribution margin ratio, so it moves with your margin. At a 40% margin, breakeven is 2.50x and a 10% profit goal needs 3.33x; at a 25% margin those become 4.00x and 6.67x. For scale, The Math documents a median brand contribution margin of ~25% across hundreds of 7-8 figure brands, so many operators' honest floor is far higher than they assume.
Because fixed costs do not move with a sale, so they cannot live inside a per-revenue-dollar target. What this calculator prices is contribution after marketing, the rung The Math calls CM3: what the order actually contributes after the cost of winning it. That pool is what pays rent, salaries and software, and the profit target is the share of revenue you want flowing into it.
Variable marketing, the same definition The Math uses: ad spend, affiliate and promo, summed across every channel for the same period as the revenue. Pull each platform's spend from its billing, not its dashboard attribution, and keep the period boundaries identical on both sides of the division.
Usually yes, and that is MER's blind spot: it is a ratio, not a size. Efficiency can rise while the total contribution pool shrinks, so a better MER can coexist with a poorer business. Read MER next to contribution dollars, never alone; this page gives you the ratio's floor, and your margin math gives you the dollars.
From one blended ratio to per-channel truth
This page runs one account-wide ratio on a blended margin. Blufire S6 Marketing & Channels computes CM1-MER and its decomposition per channel from reconciled orders, and S5 shows how attribution model choice shifts channel credit.