ROAS vs ROI vs MER: Which Marketing Metric to Trust

Short answer: ROAS tells you how much revenue each ad dollar is credited with, ROI tells you how much profit that spend actually made, and MER tells you how total revenue moves against total marketing spend, with no attribution involved. Use ROAS to steer campaigns day to day, ROI to decide whether a channel deserves budget at all, and MER to check that the whole picture still adds up.

If you’ve ever seen a campaign report a ROAS of 4 while the finance team insists marketing is losing money, both sides can be right. They’re looking at different metrics that answer different questions. This post explains each of the three, runs one campaign through all of them, and gives you a simple rule for which number to bring to which meeting.

What is ROAS, and what does it actually measure?

ROAS (return on ad spend) is revenue divided by ad spend:

ROAS = Attributed revenue ÷ Ad spend

Spend $1,000, get credited with $4,000 in sales, and your ROAS is 4 (often written 4x or 400%).

Two words in that formula carry most of the risk. “Attributed” means the revenue is whatever the ad platform or your analytics tool assigns to the campaign, using its own rules for which click or view gets credit. And “revenue” means the top line, before you’ve paid for the product, shipping or anything else.

So ROAS is a good steering metric. It’s fast, every platform reports it, and it lets you compare campaigns inside one channel. But it isn’t a measure of profit, and it isn’t a measure of what the ads caused.

What is marketing ROI, and how is it different?

ROI (return on investment) asks whether the spend made money once costs are taken out:

Marketing ROI = (Gross profit from the campaign − Marketing cost) ÷ Marketing cost

Gross profit here means revenue minus the cost of delivering it: product cost, shipping, payment and fulfilment costs. Some teams use contribution margin (gross profit minus all variable costs tied to the order), which is stricter and closer to the truth. Pick one definition and write it down; a metric definition doc saves weeks of arguing later.

The difference matters most when margins are thin. A ROAS of 3 is great for a software product with 80% margins and a loss for a retailer with 25% margins.

What is MER (marketing efficiency ratio)?

MER, sometimes called blended ROAS, zooms out to the whole business:

MER = Total revenue ÷ Total marketing spend

“Total” is the point. Every channel, every agency fee, every tool, against every sale, whether it came from an ad, an email, word of mouth or someone typing your URL from memory.

MER has a big advantage: it doesn’t depend on attribution at all. Nobody can claim credit twice, because nobody is claiming credit. The downside is the same thing seen from the other side. MER can’t tell you which channel is working, only whether the whole engine is getting more or less efficient.

A worked example: one campaign, three answers

Here’s one month for a fictional online store. The numbers are illustrative.

Input	Value
Paid social spend	$10,000
Revenue the platform attributes to it	$40,000
Gross margin	40%
Total store revenue that month	$250,000
Total marketing spend (all channels, agency, tools)	$50,000

ROAS: $40,000 ÷ $10,000 = 4.0. The platform dashboard looks healthy.

ROI: gross profit is $40,000 × 0.40 = $16,000. Subtract the $10,000 spend and divide by it: ($16,000 − $10,000) ÷ $10,000 = 60%. Still profitable, but each dollar returns $0.60 of profit, not $3 of profit.

MER: $250,000 ÷ $50,000 = 5.0 for the business as a whole.

Now the twist. The search platform also claims $35,000 of that month’s revenue, the email tool claims $30,000, and the affiliate network claims $15,000. Add every platform’s claim together and you may well get more revenue than the store actually made. Each platform credits itself with sales that other channels also touched. ROAS doesn’t lie, exactly, but every ROAS is told from the point of view of the platform reporting it.

That’s why MER is the sanity check. If every channel’s ROAS goes up this quarter but MER goes down, the channels are claiming more credit, not producing more sales.

What is break-even ROAS, and how do I calculate it?

Break-even ROAS is the ROAS at which a campaign covers its own cost, with zero profit left over:

Break-even ROAS = 1 ÷ Gross margin

With a 40% margin, break-even ROAS is 1 ÷ 0.40 = 2.5. Below 2.5, the campaign loses money on each sale even if every attributed sale were genuinely caused by the ad. Above it, you’re making money on paper.

Gross margin	Break-even ROAS
80%	1.25
60%	1.67
40%	2.50
25%	4.00

This one table explains most “but our ROAS is fine” arguments. The question isn’t whether 4 is a good ROAS. It’s whether 4 is above your break-even line, with a buffer for the share of attributed sales that would have happened anyway.

What’s a good ROAS?

There’s no universal number, and anyone who quotes one without asking about your margin is guessing. A useful way to set your own target:

Start from break-even ROAS (1 ÷ gross margin).
Add a buffer for over-attribution. If you’ve never tested how many attributed sales the ads really caused, that buffer should be generous.
Add the profit you want to keep per sale.

If you’re acquiring customers who come back and buy again, a first-purchase ROAS below break-even can still be a good deal. That’s a lifetime value question, not a ROAS question, and it’s where CAC payback period is the better metric.

Which metric should I use when?

My take: use all three, each at its own altitude.

ROAS, daily or weekly, inside a channel. Compare campaigns, ad sets and creatives against each other. The attribution bias is roughly constant within one platform, so relative comparisons are reasonable even if absolute numbers are inflated.
ROI, monthly or quarterly, per channel. Decide where budget goes. Use margin, not revenue, and ideally use incrementality-adjusted revenue, not platform-reported revenue.
MER, monthly, for the business. The check that the whole system still works. If MER holds steady while you scale spend, you’re growing efficiently. If it drops, find out why before trusting any single channel’s report.

What would change my mind: if a business has almost no organic or repeat revenue, so that nearly every sale really does come from paid media, MER and blended ROAS converge and you can lean on one number. That’s rarer than it sounds.

What none of these metrics tell you

All three measure correlation between spend and revenue, not causation. A high ROAS on a retargeting campaign can mostly reflect people who were going to buy anyway. Spend that has the highest ROAS often has the lowest incremental return.

If the budget decision is big, test it. A holdout or geo test tells you how much revenue the ads caused, which is the number ROI actually needs. I’ve written about why platform-reported conversions overstate impact and about attribution vs. incrementality vs. MMM, which covers when each method is worth the effort.

Try it on your own numbers

The free Marketing ROI Calculator works out ROAS, break-even ROAS, CAC, LTV and payback from your spend, revenue and margin, in the browser, with nothing sent anywhere. Run your best and worst campaigns through it and see which side of the break-even line they really sit on.

Frequently asked questions

Is ROAS the same as ROI? No. ROAS divides revenue by ad spend and ignores costs. ROI subtracts costs, so it measures profit. A campaign can have a ROAS above 1 and a negative ROI.

Is a ROAS of 2 good? Only if your gross margin is above 50%. Break-even ROAS is 1 ÷ gross margin, so at a 50% margin a ROAS of 2 just covers the ad spend.

What’s the difference between MER and blended ROAS? In practice they’re usually the same thing: total revenue divided by total marketing spend. Some teams limit blended ROAS to ad spend only and include agency and tool costs in MER. Write down which one you use.

Should I use gross margin or contribution margin for break-even ROAS? Contribution margin, if you can get it. It includes shipping, fulfilment and other per-order costs, so the break-even point it gives you is more realistic.

Sources

Last reviewed: 18 October 2026.

Thinking by Anthony, written with Claude.

Part of: Marketing Measurement & Experimentation

Free tools for this topic: A/B Test Calculator, Chi-Square Calculator, UTM Link Builder, Marketing ROI Calculator