What is MER (marketing efficiency ratio)?

The short answer

MER (marketing efficiency ratio) is total revenue divided by total marketing spend over the same period. $120,000 of sales on $30,000 of marketing is an MER of 4. It's the number for "is our marketing working as a whole". For "which ad should get the budget", you still need ROAS, ideally counted in your own orders.

What it is

The formula is simple: revenue for the period ÷ marketing spend for the period. A month is the usual window, since weekly numbers jump around with paydays and promos.

Here's a made-up store's October:

Both versions are in use. Polar, which sells analytics software, counts all marketing (paid media, email, SMS, agency fees) as MER, and calls revenue divided by paid media alone "blended ROAS" (Polar). Plenty of stores just use ad spend. Pick one, write it down and keep it, because a month-to-month change in definition looks exactly like a change in performance.

Which revenue to use in Shopify

Shopify gives you three sales figures, and they produce three different MERs (Shopify Help):

• Gross sales: before discounts and returns.
• Net sales: gross sales minus discounts and returns.
• Total sales: net sales plus shipping charges, taxes, duties and other fees.

Use net sales. Total sales counts the tax you pass on to the government and the shipping you pass on to the carrier, so it flatters the ratio. Gross sales ignores refunds, which flatters it too.

What it isn't

It isn't a grade for any one channel. The whole point of MER is that it ignores who gets credit. That also means it can't tell Meta from Google from your newsletter.

It isn't profit. An MER of 4 sounds healthy. At a 20% margin, it means spending $25 to make $20 on every $100 of sales. The floor for MER comes from your margin, the same maths as break-even ROAS, so work that out first.

It isn't a measure of new customers. Repeat buyers, email and word of mouth all land in the revenue line. A store with a big loyal base can show a strong MER while its ads find almost nobody new. Polar describes a variant for this, aMER: new-customer revenue divided by marketing spend (Polar).

MER or ROAS: which number for which decision

The trap is using either one for the other's job. Cutting a campaign because MER dipped is a guess. So is raising the whole budget because Meta's ROAS looks good.

Blended vs per-channel

Blended is MER's whole value. The moment you split it by channel ("Meta MER"), you have to decide which channel gets which order, and you're back to attribution with all its arguments.

Per-channel numbers come from the platforms, and each one uses its own rules. Unless you change it, Meta gives an ad the sale if the purchase comes up to 7 days after a click or 1 day after a view (Jon Loomer). Google, by default, looks back 30 days from a click (Google Ads Help). A shopper who touches both can be counted by both.

A five-minute double-count check

Add up the revenue every ad platform says it drove last month. Divide that by your Shopify net sales for the same month.

Say Meta claims $70,000 and Google claims $45,000 for the made-up store above. That's $115,000 of "ad revenue" against $120,000 of net sales, which leaves $5,000 for every returning customer, every email and every organic visit combined. Polar notes that adding up what Meta and Google report can come to more than your actual net sales (Polar). The closer that share gets to 100%, the less you should trust any single platform's ROAS.

Reading the two together

• Platform ROAS up, MER flat: the platforms are claiming more of the same sales.
• MER down, platform ROAS steady: new spend isn't bringing new sales, or the drop sits outside the ads. What to check when ROAS drops covers the order to look in.
• Spend cut, MER up, sales barely moved: the ads you cut weren't adding much.
• Both up: probably a real improvement. Check that the mix of new and returning customers didn't shift.

What a good MER looks like

There's no reliable public benchmark for small Shopify stores. The cleanest data comes from listed companies, which report revenue and marketing spend in their annual filings. eightX, a finance firm for ecommerce brands, ran nine US-listed DTC and DTC-adjacent companies' FY25 10-K figures and found MER ranging from 2.55x to 19.07x (eightX). Even there, some filers report only advertising and others report all marketing, so the numbers don't line up cleanly.

Polar calls the common "a good MER is 3 to 4" rule of thumb lazy, for the same reason: it depends on your margins (Polar). A good MER is one that stays above your margin floor while you grow. Track your own trend before you compare yourself to anyone.

Where Anry fits

MER tells you whether marketing works as a whole. Platform ROAS tells you what each platform thinks of itself. Anry sits in the gap. It traces every Meta or Google ad click through the session to whatever your store actually sold, then prices the ads and pages where money slips out. You ask it from Claude, Claude Code or Cursor, and the suggested fix is handed to your own agent there.

If you run a single channel, or your MER is steady and above your floor, a monthly spreadsheet with Shopify net sales and your ad invoices covers it.

Frequently asked questions

What is a good MER for ecommerce?

It depends on your margin. The floor is the same as break-even ROAS: 1 divided by what you keep from each sale after costs. Above that, look at your own trend. Public figures from listed DTC companies range from about 2.5x to 19x, which is too wide to use as a target.

Is MER the same as blended ROAS?

Close, and many people use the terms for the same thing. Where they differ, blended ROAS divides revenue by ad spend only, and MER divides it by all marketing spend, including agencies, email and SMS tools.

How do I calculate MER in Shopify?

Take net sales for the month from Shopify's sales report. Add up your ad spend from every platform for the same dates (plus other marketing costs if you count them). Divide the first by the second.

Should MER include agency fees?

If they're part of what it costs you to get sales, yes. The bigger rule is consistency: whatever you include, include it every month, or the trend means nothing.

What is aMER?

Acquisition MER, a name used by the agency Common Thread Collective (CTC): revenue from new customers only, divided by marketing spend. It strips out repeat buyers, so it shows how well your marketing finds new people.

Is MER better than ROAS?

Neither is better. MER is harder to inflate because it uses your own sales, but it can't split by channel. ROAS can, but each platform counts its own credit. Use MER to decide how much to spend and ROAS to decide where.

Sources

• MER (marketing efficiency ratio): the DTC metric that beats ROAS for profitability, Polar Analytics
• Analytics fields, Shopify Help Center
• Average MER by ecommerce vertical, eightX, June 2026
• Meta Ads attribution setting: a complete guide, Jon Loomer, updated March 2025
• About conversion windows, Google Ads Help
• aMER newsletter, Common Thread Collective