When a DOOH (Digital Out-of-Home) provider submits a quotation, the first figure it typically presents is network scale: number of screens, number of buildings, number of cities. Impressive numbers — but they do not answer the question every CFO and CMO ultimately needs answered:

“If I spend X amount, what do I get in return, and how do I measure it?”

This is precisely why the DOOH measurement metric system exists. Not to make reports look more sophisticated, but to transform a physical media channel into a platform that can be quantified, verified, and optimized just like any digital channel.

This article decodes that entire system — from the definition of each metric and the technologies behind data collection to a practical CPM comparison between DOOH and other popular media channels.

Core DOOH Key Metrics – Definitions and Examples

The DOOH industry uses a dedicated measurement terminology framework standardized by international organizations such as the OAAA (Out of Home Advertising Association of America) and ESOMAR. Below are the six most important metrics that every media planner should understand.

1. OTS — Opportunity To See

Definition: OTS refers to the total number of times an advertisement has the opportunity to be seen by an individual during a campaign period. An important distinction: OTS measures the opportunity for exposure, not confirmed actual viewing.

Basic formula:

OTS = Number of screens × Number of plays/day × Number of campaign days × Average footfall/screen

Practical example: A campaign runs across 50 elevator screens, with 360 plays/day for 4 weeks, in buildings averaging 200 people/day → OTS ≈ 50 × 360 × 28 × (200/360) ≈ 2,800,000 opportunities to see.

Key limitation: OTS is a potential metric — it does not distinguish between people who actually look at the screen and those who turn away. This is why more refined metrics such as VAC were developed.

2. VAC — Visually Adjusted Contact

Definition: VAC is the number of actual contacts for which there is a high probability that the viewer genuinely looked at the advertising screen. It is calculated by multiplying OTS by a Visibility Adjustment Factor.

The adjustment factor is determined based on:

• Viewing angle: A screen positioned at eye level inside an elevator cabin has a higher factor than an outdoor billboard

• Exposure time: 30–60 seconds inside an elevator vs. 2–3 seconds when driving past a billboard

• Level of distraction: A confined environment with fewer competing stimuli → elevator DOOH VAC factors typically reach 0.65–0.85, significantly higher than outdoor OOH at 0.25–0.40

Why VAC matters more than OTS: Two campaigns may have the same OTS, yet their VAC can differ by twofold if one campaign runs inside elevators — a captive environment — while the other runs on highway billboards.

3. Reach & Frequency

Reach: The number of unique individuals exposed to an advertisement at least once during the campaign period. This measures the breadth of the campaign.

Frequency: The average number of times each individual within the reached audience is exposed to the advertisement. This measures the depth of brand reinforcement.

Practical rule: Behavioral psychology research suggests that the brain requires at least 7–10 exposures to remember a new brand message. With elevator DOOH, a resident using the elevator 4–6 times per day may reach that threshold within only 2–3 days — something difficult to achieve with most other media channels.

4. Dwell Time

Definition: The average amount of time a person remains stationary or moves within the visible area of an advertising screen.

Benchmark by DOOH format:

Elevator Dwell Time is relatively short in absolute terms but particularly effective because viewers are in an enclosed environment, often without access to mobile devices in some buildings, and with few alternative visual stimuli competing for attention.

5. CPM — Cost Per Mille

Definition: CPM is the cost required to generate 1,000 advertising impressions. It is the standard metric used to compare cost efficiency across different media channels.

Formula:

CPM = (Total campaign cost / Total impressions) × 1,000

CPM serves as a common language for answering the question: “How much do I spend for every 1,000 people reached?” — and this will be examined in more detail in Section 3.

6. Conversion Lift

Definition: The incremental increase in conversion behavior — such as purchases, brand searches, or store visits — among consumers exposed to a DOOH campaign compared with a non-exposed control group.

Vietnam case study: Following an elevator-screen campaign in Ho Chi Minh City and Hanoi, Bia Saigon Special (Sabeco) recorded that 74% of surveyed respondents decided to purchase the product after seeing the elevator advertisement — a notable Conversion Lift for a traditional media channel.

The Technology Behind DOOH Measurement

The key question is: how can DOOH providers know exactly how many people looked at a screen, for how long, and who they were? The answer lies in the combination of multiple technology layers.

Data from building management

This is the most fundamental and reliable data source, collected from the stage when location contracts are negotiated:

• Number of residents/office employees: Determines the theoretical maximum audience pool

• Access card and entry control data: Provides actual traffic volume by hour and by day of the week

• Elevator operating history: Number of trips/day, peak hours, average floor-stop duration

Modern buildings equipped with BMS (Building Management System) infrastructure can export real-time elevator operating data, allowing DOOH providers to calculate OTS and VAC with significantly greater accuracy than manual estimates.

Cameras & AI-based behavioral analytics (where legally permitted)

In many international markets, smart DOOH screens integrate cameras and Computer Vision algorithms to:

• Count the number of people actually standing in front of a screen at any given time

• Analyze gaze direction through gaze tracking to estimate the proportion of people actually looking at the screen

• Identify anonymized demographic characteristics such as gender and estimated age without storing personally identifiable data — enabling optimization of content based on the actual audience profile

In Vietnam: This is a legally sensitive area. The Cybersecurity Law (No. 24/2018/QH14) and personal data protection regulations impose strict requirements on the collection and storage of biometric data. Focus Media Group — one of the world’s largest DOOH groups currently operating in Vietnam — has committed that all equipment deployed in Vietnam is camera-free, instead relying on location-based measurement and third-party data.

Independent third-party measurement

This is the technology layer that creates E-E-A-T credibility for the entire measurement framework. Rather than relying on self-reported data, reputable DOOH providers in Vietnam work with:

NielsenIQ (NIQ): Uses a combination of household surveys, retail scanner data, and statistical modeling to measure:

• Campaign Effectiveness: Increases in brand awareness and purchase intent

• Sales Lift: Actual sales growth at retail locations during and after the campaign

Kantar Media: Conducts independent studies on brand recall, brand equity, and consumer media exposure habits in specific buildings.

The presence of independent third-party measurement is what differentiates a professional DOOH provider from a vendor that merely sells “screen count” without being able to demonstrate actual effectiveness.

Programmatic DOOH & real-time data

The latest generation of DOOH integrates automated advertising buying platforms (Programmatic), enabling:

• Dynamic content changes based on real-time signals: Weather, time of day, traffic events, sports results

• Real-time impression measurement instead of only post-campaign reporting

• Cross-channel Attribution: Tracking the consumer journey from DOOH exposure → online search → purchase

In Southeast Asia, Programmatic DOOH platforms such as Vistar Media recorded 182% revenue growth in the region in 2023, reflecting the rapid shift toward data-driven measurement models.

Comparing CPM Across DOOH and Other Media Channels

CPM is the most universal metric for assessing cost efficiency. Below is a practical CPM comparison based on market data from Vietnam and the APAC region, together with specific use cases.

CPM Comparison Table

Conclusion

The DOOH industry is evolving from a “trust-based” channel — where budgets are allocated based on intuition and perceived network scale — into a media platform that can be fully quantified.

OTS, VAC, Reach & Frequency, Dwell Time, CPM, and Conversion Lift together create a comprehensive measurement system for evaluating effectiveness from multiple perspectives.

Three things every media planner should remember:

• Do not compare raw CPM alone — compare the “cost per genuinely valuable contact” by adjusting CPM according to the contact-quality factor of each channel

• Always require independent third-party measurement from organizations such as NielsenIQ or Kantar rather than relying solely on a provider’s internal reporting

• Combine DOOH with digital channels to capitalize on the “surround-sound awareness” effect — offline exposure in the elevator, followed by online reactivation through retargeting