The Ecomm Analyst

MER stands for marketing efficiency ratio. You calculate it by dividing total revenue by total marketing spend across the same period. If a store did $620,000 in revenue in July against $155,000 in marketing spend, MER is 4.0. It is deliberately crude. There is no attribution in it anywhere, which is precisely the point.

Why does MER exist when we already have ROAS?

ROAS is calculated on attributed revenue. Somebody, usually an ad platform, decided which sales belonged to which ads, and the platforms are not conservative about it. Sum the revenue Meta and Google each claim for the same month and you will frequently exceed what your store actually made.

MER sidesteps the argument entirely. Both inputs come from systems that cannot inflate themselves. Revenue comes from your commerce platform. Spend comes from your invoices. Nobody is grading their own homework. That makes MER the closest thing to a marketing metric your CFO will accept without a footnote.

What exactly goes into each side?

On the revenue side, use gross revenue before discounts and returns, or net revenue after them. I prefer net, because a MER that improves during a heavy discount month is telling you something false. Whichever you pick, hold it constant.

On the spend side, include everything that exists to drive sales. Paid media across all channels, agency fees, creative production, affiliate payouts, influencer costs, and acquisition software. Excluding agency fees is the most common shortcut, and on a store paying a $12,000 retainer against $60,000 of media it moves MER by roughly 20 percent. That is not a rounding error.

What is a good MER?

Same answer as with every efficiency ratio. It depends on your margin. A brand at 75 percent gross margin can run a MER of 2.5 and be comfortably profitable. A brand at 35 percent margin needs something closer to 5 or 6 before the business works at all.

The way to find your own floor is to work backwards. Take your gross margin percentage, subtract your fixed operating costs as a percentage of revenue, and the remainder is what you can spend on marketing before you break even. Invert that percentage and you have your break even MER. Most sub $20M brands I see land between 3 and 5.

Where MER misleads people

Three ways, and I have watched all three cause real damage.

First, MER improves when your repeat business grows, even if acquisition is getting worse. Returning customers add revenue to the numerator without adding much to the denominator. A store can post a rising MER for three straight quarters while new customer economics deteriorate underneath. Track new customer revenue separately or you will miss it.

Second, MER lags. Spend today produces revenue over the following weeks, so a month where you scaled hard on the 20th will show a depressed MER that recovers in the next period. Reading a single month in isolation invites panic cuts. I look at a rolling 60 or 90 day figure alongside the monthly one.

Third, MER tells you nothing about allocation. It is a thermostat, not a map. It will tell you the room is too cold. It will not tell you which window is open. When MER drops, you still need channel level diagnostics to find out why, and that is where an attribution tool earns its keep. ThoughtMetric, which sponsors this blog, pulls ad platform spend and Shopify order data into one view so the channel breakdown sits next to the blended number rather than in a separate export.

Should MER replace ROAS?

No. They answer different questions. MER answers whether the marketing function as a whole is paying for itself. Platform ROAS answers whether a specific campaign is worth more budget, subject to attribution assumptions you should treat with suspicion.

Run MER as the number that governs total budget. Run channel ROAS as the number that governs how that budget is split. The failure mode is using either one for the other job. I laid out how the three efficiency numbers relate in MER, blended ROAS, and platform ROAS.

How I actually use it

I set a MER floor tied to break even, then a target roughly 20 percent above it to leave room for fixed cost growth. If the rolling number holds above target, spend goes up. If it breaks the floor for two consecutive weeks, spend gets held while I look at the channel data.

That is a boring policy, and boring is the value. MER is not a clever metric. It is an honest one, and honest beats clever when you are deciding how much money to put into the market next month.