MER vs ROAS: Which Metric Actually Fits Your Business

ROAS vs. MER shouldn’t be an argument.

It’s a choice.

The right question is: which one actually fits your business model?

The debate usually goes like this.

Someone says ROAS is broken.

Someone else says MER is too vague.

Both are partially right.

But they're arguing in the abstract, which is why nothing gets resolved.

The truth is simpler.

ROAS works well in some situations.

MER works better in others.

The mistake is applying either one universally.

Let me give you two real examples.

You run Meta ads to generate leads.

Potential clients fill out a form, land in your CRM, and a sales team follows up and closes the deals.

Revenue shows up days, weeks or months later.

Tracking ROAS here is hard and ad spend falls apart immediately.

Meta sees the lead, not the closed deal. If your ad spend was €5,000 and Meta shows you a ROAS of 1.2x, that number means almost nothing.

You don't sell leads. You sell the outcome of those leads.

What you actually need to know:

Spent €5,000. Closed €30,000 in contracts.

MER is 6. That's a number you can actually make decisions with.

ROAS in this model is a distraction.

It measures something Meta can see, not something that matters to your business.

I covered how MER works in detail back in DAS #95 - The one Metrics that shows if your marketing is actually working.

You run an ecommerce store.

Three products. Customer clicks the ad, lands on the product page, buys.

The whole journey happens online, usually in one session.

Here, ROAS is actually useful.

You know your margins.

You know what you need to bring in per euro spent to stay profitable.

Attribution is reasonably clean because the purchase happens in the same session as the click.

Set your target ROAS at 3x and above, and you're running with a profit buffer.

Drop below break-even and you know immediately.

ROAS gives you something to optimize against at the campaign and ad set level.

It tells you which creative is pulling weight, which product angle converts, where to push budget.

In this model, ignoring ROAS in favor of MER alone would mean losing the granular signals that actually help you improve performance day to day.

Ask yourself one question: does the sale happen online, in one session, with clean attribution?

Most businesses need both, but with different weights.

A lead gen business uses MER to judge overall efficiency and ROAS as a rough directional signal at best.

An ecommerce brand uses ROAS to optimize campaigns and MER to check that the business as a whole is healthy, not just the ad channel.

The mistake I see most often: ecommerce brands tracking MER too loosely and ignoring when a specific channel is quietly burning cash.

Or lead gen businesses chasing a ROAS target that has no connection to how their revenue actually works.

One more thing. If your ROAS looks great but MER is weak, something is off.

Maybe you're measuring partial attribution.

Maybe your organic or email revenue is masking underperformance in paid.

Or maybe your COGS and other costs changed and it’s eating your profit margin on the backend.

MER catches that. ROAS doesn't.

For the full ROAS breakdown, read DAS #10 - Why Facebook Ads ROAS is a misleading metric.

This issue is about the decision between them.

And the decision is simpler than most people make it.

Match the metric to how your business actually makes money.

Everything else is noise.

TLDR