ROAS is one of the most quotable metrics in performance marketing, and one of the most often misread. It answers a simple question: how much revenue do I get for every euro I put into advertising? This article explains the calculation, the difference to ACoS and above all how to use ROAS to make smarter budget decisions.

What ROAS means

ROAS stands for return on advertising spend, the return per advertising euro invested. The formula:

ROAS = ad-attributed revenue ÷ ad spend

An example: you spend €250 on a campaign and it brings in €1,250 in revenue. Your ROAS is 1,250 ÷ 250 = 5. Every euro invested brought €5 in revenue. ROAS is often written as a ratio (5:1) or as a percentage (500%) too.

ROAS and ACoS: two sides of the same coin

ROAS and ACoS describe exactly the same relationship, only inverted. ACoS expresses the ad cost as a percentage of revenue, ROAS expresses the revenue as a multiple of the cost. You can convert between them:

  • ROAS = 1 ÷ ACoS (as a decimal)
  • An ACoS of 20% is a ROAS of 5.
  • An ACoS of 25% is a ROAS of 4.
  • An ACoS of 50% is a ROAS of 2.

Which metric you prefer is ultimately habit. People who come from classic online marketing tend to think in ROAS, people who grew up with Amazon in ACoS.

The most common mistake: reading ROAS without the margin

A high ROAS always sounds good, and without your margin the number is worthless. What counts is the break-even ROAS, the point at which your advertising covers its cost. It follows from your margin.

A worked example: your product has a 25% margin after every cost. Your break-even ROAS is then 1 ÷ 0.25 = 4. A ROAS of 4 therefore means break-even. Only above a ROAS of 4 do you earn money on advertised sales, below it you pay in.

That explains why "a ROAS of 3 is bad" need not be true: at a 40% margin (break-even ROAS 2.5) a ROAS of 3 would be profitable.

Using ROAS sensibly as a steering figure

ROAS becomes useful once you look at it in parts rather than as one total:

  • By campaign type: brand keywords almost always deliver a high ROAS, because purchase intent is high. That tempts people to push budget only there, even though those buyers would often have found you anyway.
  • By funnel stage: discovery campaigns (broad keywords, new audiences) naturally have a lower ROAS than conversion campaigns. Measuring them against the same target would be a mistake.
  • Over time: a single day says little. Judge ROAS over one to two weeks to average out the swings.

The limits of the metric

Like ACoS, ROAS only counts ad-attributed revenue, not the organic effect of your ads. A campaign with a low ROAS can still be valuable if it pushes your ranking and pulls organic sales behind it. So the same rule applies: add a whole-business view (TACoS, for instance) before you switch off a supposedly "weak" campaign.

Practical steps

First calculate your break-even ROAS per product, because that is your zero line. Then set realistic targets above it depending on the campaign's job (higher for conversion, lower acceptable for discovery). Only compare campaigns within the same funnel stage. And before every budget cut, check whether the campaign in question is carrying organic revenue too.

In short

ROAS is an intuitive, strong metric, but only with margin and context. The break-even ROAS from your margin is the yardstick everything measures against. Whoever reads ROAS separately by campaign type and funnel stage, and does not forget the organic effect, steers their ad budget far more precisely than someone chasing one blanket target.