ROAS vs. ACoS: Which Metric Matters on Amazon?

What is ACoS?

ACoS (Advertising Cost of Sales) indicates what share of your ad revenue you spent on advertising. The formula is simple:

ACoS therefore answers the question: How many cents of every advertising dollar did I have to spend on the ad itself? At an ACoS of 25%, 25 cents of every dollar earned flow back into advertising.

ACoS is the standard metric in Amazon Seller Central and in the Amazon advertising dashboard. When Amazon sellers talk about their PPC performance, they almost always use ACoS. It is intuitive: the lower the ACoS, the more efficiently the campaign runs. An ACoS of 10% means you spend only 10% of your ad revenue on advertising. An ACoS of 50% means half is consumed by ad costs.

What is ROAS?

ROAS (Return on Ad Spend) flips the perspective. Instead of asking what percentage of revenue goes to advertising, it asks: How much revenue do I get back for every advertising dollar invested?

ROAS is often expressed as a simple number (e.g. 4.0) or as a ratio (4:1). Some tools also present it as a percentage (400%), though that is less common.

While ACoS dominates within the Amazon ecosystem, ROAS is the preferred metric in the broader advertising world. Google Ads, Meta Ads and most performance marketing platforms use ROAS as their primary efficiency metric. So if you also advertise outside Amazon, you will already know ROAS.

The mathematical relationship: ACoS and ROAS are reciprocals

Here lies the key to understanding: ACoS and ROAS are mathematical reciprocals of each other. If you know one value, you can immediately calculate the other.

Let's look at this with concrete numbers:

ACoS	ROAS	Meaning
10%	10.0	Very efficient. $10 in revenue per $1 of ad spend.
20%	5.0	Solid performance. $5 in revenue per $1 of ad spend.
25%	4.0	Typical value in many categories.
33%	3.0	Acceptable with good margins.
50%	2.0	Borderline. Only profitable with very high margins.
100%	1.0	Break-even at the revenue level (excluding other costs).

This table shows: it is exactly the same information, just presented differently. An ACoS of 25% and a ROAS of 4.0 describe identical campaign performance.

How Amazon displays the metrics

By default, Amazon shows ACoS in the advertising dashboard and in reports. This is because Amazon introduced the metric itself and it is considered the standard in the seller community.

ROAS, however, also appears in the Amazon world. In the Amazon DSP (Demand Side Platform) it is used as the primary metric. You will also find ROAS as an additional column in newer versions of the Amazon advertising console. If you use the Advertising API or work with tools like Sellantica, you usually have access to both values.

In the downloadable reports (Sponsored Products report, Sponsored Brands report) you will find ACoS as a standard column. You can either add ROAS there as a column or calculate it yourself by dividing the "Sales" column by the "Spend" column.

When you should use ACoS

ACoS is the better choice in the following situations:

• Communicating with other Amazon sellers: in the Amazon community, ACoS is the established standard. When you talk about performance in forums, mastermind groups or with your agency, everyone immediately understands what an ACoS of 20% means.
• Comparing with your profit margin: ACoS can be compared directly with your gross margin. If your margin is 30% and your ACoS is 25%, you know immediately that after deducting ad costs, 5 percentage points of profit remain (before further costs such as FBA fees, overhead, etc.).
• Defining a target ACoS: ACoS is often more practical for campaign management. You can calculate your break-even ACoS and derive a target ACoS from it that serves as a concrete upper limit for your bids.
• Working in Amazon Seller Central: since Amazon itself uses ACoS as the primary metric, you save yourself unnecessary conversions.

When you should use ROAS

ROAS has its strengths in other contexts:

• Cross-channel comparison: if you advertise on Google, Meta or other platforms in addition to Amazon, ROAS enables a direct comparison. You can immediately see which channel generates the most revenue per dollar invested.
• Communicating with stakeholders: investors, executives and marketing decision-makers outside the Amazon world think in ROAS. A ROAS of 5.0 says: "For every dollar we invest, five dollars come back." That is easier for non-specialists to grasp.
• Justifying budget: in budget negotiations, ROAS is often more convincing. "Our ROAS is 4.0" sounds like a solid return. "Our ACoS is 25%" requires an explanation of whether that is good or bad.
• Scaling decisions: when you consider which channel to put more budget into, ROAS provides the clearer answer. Channel A with a ROAS of 6.0 deserves priority over channel B with a ROAS of 3.0.

Practical examples with concrete numbers

Let's work through two realistic scenarios to illustrate the application of both metrics.

Scenario 1: Profitability check

You sell a product for $29.90. After deducting cost of goods, FBA fees, Amazon commission and shipping, you are left with $9.00 gross margin per unit. Your margin is therefore around 30%.

Your campaign shows the following values:

• Ad spend: $300
• Ad revenue: $1,500
• ACoS: 300 / 1,500 = 20%
• ROAS: 1,500 / 300 = 5.0

Since your ACoS (20%) is below your gross margin (30%), the campaign is profitable. You keep 10 percentage points (about $150) as profit after ad costs. With ROAS alone, this assessment would be harder, because you would first have to calculate the ROAS at which you become profitable (in this case: 1 / 0.30 = 3.33).

Scenario 2: Channel comparison

You advertise on Amazon and on Google Shopping. Last month's numbers:

Channel	Ad spend	Revenue	ROAS	ACoS
Amazon PPC	$2,000	$8,000	4.0	25%
Google Shopping	$1,500	$5,250	3.5	28.6%

Here ROAS shows at a glance that Amazon performs more efficiently. To reach the same conclusion with ACoS, you would have to recognize that 25% is better than 28.6%. Both work, but ROAS makes the comparison more intuitive, because "higher = better" applies, whereas with ACoS the logic is "lower = better."

Common thinking errors and misconceptions

Although ACoS and ROAS are mathematically simple, there are a number of widespread thinking errors:

Thinking error 1: "A low ACoS is always better"

An ACoS of 5% sounds dreamy. But if you only generate $100 in ad revenue per month with it, you are leaving enormous growth potential on the table. An ACoS of 25% on $10,000 in revenue generates more absolute profit than an ACoS of 5% on $100 in revenue.

Efficiency alone says nothing about volume. Sometimes it makes strategic sense to accept a higher ACoS in order to gain more market share.

Thinking error 2: "ROAS and profit are the same"

A ROAS of 5.0 does not mean you make $5 of profit per dollar invested. ROAS refers to revenue, not profit. From those $5 of revenue, cost of goods, Amazon fees, FBA costs and other expenses still have to be deducted. Only once you subtract all of that do you know whether the campaign is really profitable.

Thinking error 3: "An ACoS above 100% is always a disaster"

At an ACoS of 120%, you spend more on advertising than you earn from it. At first glance that is bad. But there are situations where it makes strategic sense: during a product launch, for example, when you want to build reviews and gain organic ranking. The short-term loss can pay off long-term through better organic visibility.

Thinking error 4: "ACoS and TACoS show the same thing"

ACoS only considers ad revenue. TACoS (Total Advertising Cost of Sales) relates ad spend to total revenue, i.e. including organic sales. TACoS is therefore almost always lower than ACoS and gives a more realistic picture of overall profitability.

Conclusion: which metric should you use?

The honest answer: both. ROAS and ACoS provide exactly the same information, packaged in different perspectives. The choice depends on your context.

If you advertise exclusively on Amazon and communicate with other Amazon sellers, stick with ACoS. It is the established standard, Amazon displays it prominently, and you can compare it directly with your margin.

If you think across channels, distribute budgets over multiple platforms or communicate with stakeholders who are not at home in the Amazon ecosystem, use ROAS. It is universally understood and makes comparisons easier.

Most important is that you understand the relationship between the two metrics and avoid the typical thinking errors. Those who master the basics make better decisions, whether the focus falls on ACoS or ROAS.