How ROAS is calculated in retail media
Return on ad spend divides the sales attributed to your ads by what those ads cost to run. In Amazon's own worked example, $50 of ad spend that brings in $100 of attributed sales is a ROAS of 2.0. ROAS can also be written as a ratio, as Amazon does (2:1), or as a percentage (200%).
Attributed sales are the purchases a network credits to an ad within its attribution window, and the IAB/MRC retail media guidelines tie them to the SKUs in the ad. The guidelines also require networks to disclose whether those sales rest on viewable impressions or on extrapolation.
ROAS is the inverse of advertising cost of sales (ACOS), so Amazon's $50 and $100 example is a 50% ACOS.
How to set a target ROAS
Start from break-even. Amazon ties break-even ACOS to profit margin, and ROAS is ACOS inverted, so break-even ROAS is 1 divided by the margin before advertising. A product with a 25% margin breaks even at a ROAS of 4.0. Above that line the ads earn back their cost with margin to spare, and below it they lose money.
Profit campaigns sit above break-even. A launch, a new-to-brand push, or a defense of search visibility can justify a lower target, and Amazon notes that new campaigns tend to run a high ACOS, which is a low ROAS, because they are new. Because margins differ by product, set targets per SKU or per margin tier. A refurbished-electronics reseller on Walmart Connect tiered its bids by product performance and finished above its target ROAS.
Amazon's rule-based bidding can then adjust bids around a ROAS guardrail you set, such as Amazon's example of 3. Auto-bidding vs manual bidding covers the trade-offs.
ROAS across retail media networks
ROAS figures from two networks can measure different things. The IAB/MRC guidelines note that attribution windows are often 3, 7, 14, 28, or 30 days, require networks to disclose them, and encourage consistent windows plus day-level data for reconciliation.
Take a brand that sells one SKU as an Amazon vendor and on Walmart Connect. Amazon Sponsored Products counts sales within 14 days of a click for Vendor Central accounts (7 days for Seller Central) and credits the last ad clicked. Walmart Connect reports click-based attributed sales over a 3, 14, or 30-day window. Compare a 14-day Amazon figure with a 30-day Walmart figure, and the higher ROAS may reflect the longer window. Put both on the same window before moving budget.
Closed-loop attribution explains how retailers tie ad exposure to sales. The Walmart Connect guide and our retail media network profiles cover each network.
What ROAS does not measure
ROAS counts attributed sales, including purchases that would have happened without the ad. The IAB/MRC guidelines define incrementality as the value above and beyond that baseline. By that definition, a campaign that mostly reaches shoppers who already buy the brand can report a high ROAS while adding little incremental value.
Campaigns built to win new buyers face the opposite problem. "If you're trying to bring new buyers to your brand, ROAS is probably not the right metric to measure against," The Trade Desk's Ben Sylvan told Programmatic I/O's 2024 Retail Media Summit. Whether those buyers come back is a customer lifetime value (CLV) question, which a single-purchase ROAS cannot answer.
The IAB/MRC explainer recommends exploring metrics that capture campaign impact more appropriately than ROAS, such as new-to-brand, category share growth, or digital shelf share.
Why it matters for brands and sellers
ROAS is the number budgets move on, so the window, the attributed-sales rules, and the SKU scope behind it decide where money goes, both between networks and between SKUs. A longer window can raise one network's ROAS without any change in performance, and a campaign-level ROAS blends SKUs with different margins. The IAB/MRC guidelines ask for SKU-level reporting where relevant, since most retail media spend promotes specific products.
ROAS is also easy to act on: Walmart Connect's Sponsored Search dashboards show it beside impressions, clicks, and sales. Before moving money on it, set a break-even ROAS per product from its margin, align windows across networks, and read ROAS next to incremental or new-to-brand results when you plan your retail media budget.
Related terms
- Advertising cost of sales (ACOS): ROAS inverted, with the full comparison table.
- Incrementality: the sales a campaign actually caused.
- Closed-loop attribution: how retailers link ad exposure to sales.
- Product margins: the input to break-even ROAS.
- Auto-bidding vs manual bidding: where a ROAS target becomes automation.
- Customer lifetime value (CLV): the long-run value one purchase leaves out.
Frequently asked questions
How do you calculate ROAS?
Divide attributed sales by ad spend. In Amazon's example, $50 of spend that brings $100 in attributed sales is a ROAS of 2.0, also written 2:1 or 200%. Then check the network's attribution window, which sets how long after exposure a sale still counts.
What is a good ROAS in retail media?
No single benchmark fits every brand. For a profit goal, a good ROAS clears break-even, which is 1 divided by the product's margin before advertising. New campaigns can run below it, since Amazon notes they tend to have a high ACOS. Compare networks only on the same attribution window.
Is a ROAS of 4 good?
A ROAS of 4 is profitable only when the product's margin before advertising is above 25%. At a 25% margin, 4.0 is exactly break-even, the same point as a 25% ACOS. At a lower margin, each attributed sale costs more in advertising than it earns.
What does ROAS stand for?
ROAS stands for return on ad spend. Amazon Ads describes it as a metric that measures a specific ad campaign and how it has affected revenue. In retail media marketing, it means attributed sales per dollar of ad spend, counted within the network's attribution window.
