Return on ad spend looks like the obvious metric for retail media — and it’s usually the wrong one to lead a conversation with a retailer, even when the number is genuinely good.
Why ROAS alone misleads
A high ROAS can simply mean you’re bidding on shoppers who were already going to buy your product anyway — you’ve paid to capture a sale you’d have made for free. Retailers care about incremental sales the spend actually created, not sales the ad happened to sit alongside. Two campaigns with identical ROAS can have completely different real value.
The metric that changes the conversation
Incremental share of category shift during the campaign window, compared to a control period, is a far harder number to produce — but it’s the one that actually earns a bigger budget conversation next time. Brands that can show “we grew category share by X points, not just sold more of our own units” get treated as a genuine growth partner rather than an advertiser buying space.
What to ask for from your retail media partner
Push for category-level reporting, not just brand-level, even if it’s harder to get. Most retail media platforms can produce it if asked directly — most brands simply never ask, and default to the easier, less persuasive number.
Not sure if your retail media reporting is measuring the right thing?
Steven Woodgate, Founder, Emmer Green — former Head of Category (Technology), John Lewis & Partners; former senior commercial leadership roles at Samsung, Dell Technologies and Microsoft.
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