Retail media has become one of the fastest-growing areas of digital advertising, with the sector continuing to expand at a clip of ~30% year over year. As brands increase their investment in retail media networks (RMNs), expectations around performance measurement have grown just as quickly.

But evaluating retail media performance isn’t always straightforward. Different platforms within the stack measure success in different ways. Some focus on engagement metrics like clicks while others measure campaign impact based on transactions.

This raises an important question as retail media programs mature: what should success actually be measured against?

Retail media’s promise was always closed-loop measurement

Retail media emerged with a unique advantage over other digital channels: visibility into actual purchase behavior. Because retailers own both the media environment and transaction data, they can connect ad exposure to real sales outcomes. This ability to close the loop between media and commerce is one of the main reasons brands continue increasing investment in retail media. As the ecosystem grows, however, how performance is measured has become less straightforward.

Why engagement metrics became the industry default

Clicks historically became the standard performance signal across digital advertising. They were practical because early digital environments lacked access to transaction data. Engagement metrics provided a real-time signal of interaction, which helped marketers optimize campaigns quickly. Clicks are useful signals, but they measure interaction with media—not necessarily business outcomes.Retail media operates in a different environment than traditional digital advertising.

Retail media operates with a different data advantage

Retailers can see actual transactions, not just engagement signals. First-party data has the potential to connect shopper identity, media exposure and purchase behavior. In theory, this connection is what gives retail media its unique advantage. In practice, however, it is also where many retail media programs encounter challenges. Maintaining a consistent link between shopper identity, ad exposure and purchase activity often requires coordination across multiple systems responsible for activation. When those signals become fragmented as data moves between platforms, the ability to tie media exposure back to transactions can weaken.

However, when these remain connected, retailers and brands gain the ability to evaluate campaigns based on their contribution to sales. This creates the potential for closed-loop measurement, where performance reflects real purchasing behavior rather than engagement proxies. Despite this advantage, many retail media programs still rely heavily on engagement metrics. This creates a gap between what retail media can measure and what it is often measured by.

The measurement gap facing many retail media programs

Many RMN stacks include multiple partners measuring different signals. Some platforms measure clicks or impressions, while others measure transactions. When success is defined differently across platforms, comparison becomes difficult.

In practice, these differences often reflect how each technology platform is designed to optimize media performance. A demand-side platform may report metrics such as CPM efficiency, viewability rates or click-through rate. Search-based retail media tools often emphasize cost-per-click, keyword performance and conversion rate. Retail media platforms with access to transaction data may instead report return ad spend tied to verified purchases.

When these signals are presented together, retailers and advertisers may find themselves comparing engagement-based outcomes. This can make it difficult to determine which campaigns are truly driving business impact, particularly when different partners optimize different success signals.

Why sales measurement changes the conversation

Sales measurement connects media investment directly to business impact. It allows brands to evaluate ROI in terms that align with their core objectives. Transaction-based measurement supports more accurate optimization and planning.

For many advertisers, engagement metrics such as click-through rate or cost per click are still useful signals for monitoring campaign activity and making day-to-day optimizations. But those signals are often only proxies for the outcome advertisers ultimately care about: whether media investment is influencing real purchases.

Retail media is uniquely positioned to bridge those two perspectives. Engagement metrics can help explain how shoppers interact with advertiser, but the true advantage of retail media lies in its ability to connect those interactions to verified transactions. As retail media grows in scale and complexity, aligning measurement with purchase outcomes becomes increasingly important.

Measurement will become more important as retail media expands

Retail media is expanding across onsite, offsite and in-store channels. The number of platforms and data sources involved in campaigns is increasing. As the ecosystem grows, shopper journeys become more complex. A consumer may encounter an ad on a retailer’s website, see related messaging through offsite media and ultimately complete a purchase through a mobile app or physical store.

Each interaction can influence the outcome, but connecting those touchpoints requires consistent identity and reliable data signals across environments. As RMNs extend campaigns beyond their owned properties, maintaining visibility into the full path to purchase becomes more challenging.  Measurement approaches that preserve the connection between media exposure and purchase behavior will play a larger role in evaluating retail media performance as these environments evolve.

Aligning retail media measurement with its core objective

Retail media exists to help brands reach shoppers and drive product sales. Engagement metrics can provide useful signals along the way. But the defining advantage of retail media remains its ability to connect advertising directly to transactions. As the ecosystem matures, aligning measurement with that outcome will become increasingly important for retailers and brand partners alike.

As retail media continues to evolve, the conversation around measurement is likely to become more nuanced. Engagement metrics will continue to play a role in helping marketers understand how shoppers interact with media and where optimization opportunities may exist. But as retail media programs grow in scale and sophistication, retailers and brand partners will increasingly look for measurement approaches that connect media activity to the outcomes that matter most for their businesses.

Retail media’s defining advantage has always been its ability to link advertising exposure to real purchase behavior. Preserving that connection as the ecosystem expands—across platforms, partners and channels—will be critical to maintaining trust, demonstrating value and sustaining long-term growth. For retailers and brands alike, aligning measurement with that core objective will remain central to realizing retail media’s full potential.

To learn more about the role of identity in enabling closed-loop measurement in retail media, explore IDC’s White Paper, sponsored by Epsilon, Identity Drives End-to-End Retail Media Outcomes.