Out-of-home advertising, both OOH and DOOH, is primarily purchased to create reach and generate the right level of pressure within a defined target audience. Consequently, three base metrics are used in almost all planning: reach, frequency, and GRP. These are standard in international guidelines and recognized by industry organizations, such as the OAAA and in JCDecaux’s own guides to (D)OOH measurement.

What do reach, frequency, and GRP mean in (D)OOH?

In (D)OOH, these are defined as follows:

• Reach: The proportion of individuals in the target audience exposed to the campaign at least once during the campaign period.

• Frequency: The average number of exposures per reached individual.

• GRP (Gross Rating Points): The product of reach and frequency, often expressed as rating points over time.

Billups describes these as the foundation for planning and comparing OOH campaigns: reach tells you how many people, frequency tells you how often, and GRP provides a comprehensive view of the campaign’s total pressure. The OAAA’s own glossary defines GRP in (D)OOH as a key metric for campaign delivery and for modeling reach and frequency.

How are reach and frequency built in practice?

There are two primary ways to build reach in (D)OOH:

1. Geographic dispersion: Spreading units across multiple areas, neighborhoods, or cities.

   • Result: More unique individuals are reached → reach increases.

2. Concentration in key hubs: Placing units heavily where traffic flows are high and visibility is strong (hubs, city centers, premium sites).

   • Result: Frequency increases relatively faster than reach; i.e., the same individuals encounter the message multiple times.

GRP serves as a tool to balance these effects. Vector Media describes it as a practical compass: should the campaign prioritize reaching as many people as possible (reach) or increasing the number of contacts among those already reached (frequency), given a specific GRP target?

DOOH: Reach and frequency in shared loops

In DOOH, an additional dimension enters the equation: a single screen carries multiple campaigns in a shared spot loop. This means that reach and frequency are governed by both:

• Number of screens and their placement.

• Share of loop: The percentage of the loop your campaign occupies, and during which hours.

At JCDecaux and across the industry, we emphasize that the flexibility of DOOH allows you to:

• Concentrate pressure during specific hours or days when the target audience is most present.

• Dial up the frequency during defined windows (e.g., launch week, evenings, weekends) without needing to change physical sites.

The result is that you can build high frequency among the right people rather than spreading pressure evenly throughout the day.

Best formats for (D)OOH reach, where the “big picture” is crucial

When planning the best formats and networks for reach in (D)OOH, you must consider the big picture:

• A broad network of standardized sites: Provides a stable base reach and ensures that a large portion of the target audience is reached at least once.

• Select sites and premium locations: Used for reinforcement around high-priority areas, such as city centers, retail districts, or transit hubs, where both reach and frequency can be built more rapidly.

• Placement and overlap: By understanding how different traffic flows and locations overlap, you can:

  • Avoid overexposure within certain segments of the target audience.

  • Free up space to add new contacts in other segments.

As Cecilia Ottobre, Sales Director at JCDecaux Sweden, states: “It is the interaction between reach, frequency, and GRP that makes (D)OOH planning effective, not the maximization of a single number.”

Conclusion: Steer toward the right combination, not just high numbers

• Reach tells you how many people in your target audience you reach.

• Frequency tells you how often they are reached.

• GRP connects the two, making it possible to compare campaigns over time and across media.

By combining a broad network of sites with the smart use of “select” and premium formats—and, in DOOH, the right share of loop at the right time—you can steer toward a level where reach, frequency, and GRP support the campaign’s purpose and its role in the media mix, rather than simply chasing the highest possible number of contacts.