Blended ROAS and marketing efficiency ratio (MER) explained

The simple formula

Marketing efficiency ratio, usually shortened to MER, is total revenue divided by total marketing spend for the same period. If your store took in $31,000 last month and you spent $10,000 across every ad platform, agency fee and promotion, your MER is 3.1. Many people call the same number blended ROAS, because it blends all channels into one return on ad spend.

The key word is total. Revenue comes from your own records, such as Stripe payments, store orders or invoices. Spend includes every channel you paid for, not just the two you check most often.

Why adding up platform ROAS goes wrong

Each ad platform reports the sales it believes its ads influenced. A shopper might see a Meta ad on Monday, click a Google ad on Wednesday and buy. Both platforms can count that one sale, each inside its own attribution window, the period after a click or view during which a sale is credited to the ad (attribution windows explained).

So when you add the platforms' numbers together, the total is often bigger than what landed in your bank account. In the worked example on this page, Meta reports a 4.0x ROAS and Google reports 4.5x. Their combined claims come to $42,000 of sales on $10,000 of spend, or 4.2x. The store actually took in $31,000, so the true blended figure is 3.1x. Nobody lied. Each platform simply measured from its own point of view.

MER sidesteps that problem because it never asks who gets credit. It only asks how much came in and how much went out.

What MER is good for, and what it hides

MER is the number to watch for the health of the whole business. It is hard to fool and easy to explain to an owner, partner or client. It also captures effects that platform reports miss, such as people who saw an ad, searched for your name later and bought without clicking anything.

That breadth is also its weakness. MER includes sales that would have happened with no ads at all: repeat customers, word of mouth, a mention in the press. A rising MER might mean your ads improved, or it might mean a busy season lifted everything. And it cannot tell you which channel to cut, because every channel is blended in.

• Use MER to judge whether total marketing spend is paying off, week to week and month to month.
• Use platform ROAS to compare campaigns and ads within a single channel.
• Use tests that switch spend on and off to learn what each channel truly adds (incrementality testing).

What a good MER looks like

There is no universal good MER, because it depends on your margins. The minimum you need is your break-even point: one divided by your gross margin, the share of each sale left after paying for the product. A business with a 50% margin needs an MER of at least 2 before marketing covers its own cost. Below that, every extra dollar of spend loses money before overhead. Our break-even ROAS guide walks through it.

Many businesses also track new-customer MER: revenue from first-time buyers divided by spend. It strips out repeat buyers who might have come back anyway, so it is a stricter test of whether ads are bringing in new people.

Spend is shifting toward the channels that claim the most credit

Getting the blended view right matters more as budgets move. Gartner's 2026 marketing survey found that awareness and conversion now account for 62.6% of total media spend, and that digital media makes up more than two-thirds of media investment in 2026, up 18% since 2024. The survey covered 401 marketing leaders, most at companies with more than $1 billion in revenue. More money in digital channels means more platforms reporting their own version of the truth.

To calculate MER by hand, export each platform's spend, add it to your other marketing costs, and divide your real revenue for the same dates by the total. Keep the dates and the currency consistent. Matrix ROI, a product of Smith App Studio, does this side by side every day: what each platform claims next to what your payments verify, in one currency.