OOH Metrics Explained: A Guide to Impressions, Reach, CPM, and More

If you’re exploring out-of-home (OOH) advertising for the first time, you’re in the right place. Whether you're placing your brand on a billboard, or transit shelter, understanding a few key terms can make a big difference in how effectively you plan and measure your campaign. Let’s get started!

Impressions: Estimating Visibility

In OOH, impressions refer to the number of times your campaign will be seen. Impressions aren't just based on raw traffic counts, they’re refined using data on visibility, movement patterns, and demographic filtering. For example, a digital billboard on a busy highway could generate hundreds of thousands of impressions weekly, based on how many cars pass, the speed of traffic, and the ad’s visibility window.

Reach and Frequency: Breadth vs. Depth

Reach measures how many unique individuals are exposed to your ad during a campaign, while frequency tracks how often the average person sees it. Together, they determine the overall impact of your media plan: reach ensures your message touches a broad audience, and frequency helps reinforce it through repeated exposure. The right balance depends on campaign goals - whether building mass awareness, driving recall, or both.

High-frequency OOH campaigns are powerful for driving recall and influencing decisions. People might pass a billboard campaign many times in a week, building and reinforcing brand awareness to prime the audience to prefer the advertised brand before they’re ready for purchase. Learn more about why frequency is considered OOH’s ‘superpower’ in this piece by our CMO, Dan Levi.

CPM: Comparing Value Across Channels 

CPM stands for Cost Per Thousand impressions and helps you evaluate media efficiency. It's a standard way of comparing the value of different media types and is calculated by dividing the total cost of your campaign by the number of impressions (in thousands). OOH often has highly competitive CPMs compared to digital, TV, or radio - especially when you factor in the large-scale visibility and lack of ad blockers or skip buttons. But CPM isn’t everything. The impact and context of OOH, its ability to reach people in the physical world, close to moments of decision, adds meaningful value that’s hard to capture with CPM alone.

Proximity Targeting: Location-Based Precision

One of OOH’s biggest advantages is proximity targeting: strategically placing ads near stores, events, or even competitors. This is particularly valuable for retailers, healthcare providers, QSR chains, auto dealers, service businesses and other companies for whom location is important. CCO uses privacy conscious behavioral and movement data to select optimal locations based on where your audience lives, works, and shops; bringing your message closer to where decisions happen.

Indexing: Where Your Audience Shows Up

When we say a location “over-indexes”, it means your target audience is more likely than average to be there. For instance, if young professionals over-index in a particular urban neighborhood, that area might be ideal for promoting a mobile career platform or energy drink. CCO’s audience planning solution, RADARView, helps marketers discover where key audience segments index high or low, so you can match your message to the right places.

Why It All Matters

OOH is no longer just about eyeballs, it’s about reaching the right audience most efficiently and providing measurable performance. When used together, impressions, reach, frequency, CPM, proximity, and indexing allow marketers to plan smarter, compare across media, and drive tangible results.