Outdoor advertising was historically the hardest medium to measure. That has changed dramatically. Today, OOH can be measured by DEC (Daily Effective Circulation), GRP (Gross Rating Points), CPM (Cost Per Thousand), and increasingly by mobile device proximity data. In India, the IOAA's Roadstar is the approved standard. Globally, Geopath is the leading system.
OOH measurement uses its own vocabulary. These are the terms you will encounter in any OOH media plan:
| Metric | What it measures | Formula / Notes |
|---|---|---|
| DEC Daily Effective Circulation | Estimated number of people who pass a board per day | Traffic count (PCU) × occupancy factor × adjustment for direction & visibility |
| OTS Opportunity To See | Number of times the target audience could see the ad (does not confirm they actually looked) | DEC × campaign days |
| LTS Likely To See | Adjusted OTS based on eye-tracking data — how many people actually looked at the board | OTS × Visibility Adjustment Index (VAI). VAI from Geopath eye-tracking research. |
| GRP Gross Rating Points | Total campaign delivery as % of target market population | GRP = (DEC ÷ Market Population) × 100 × Campaign Days ÷ 7 × Days per week |
| CPM Cost Per Thousand | Cost to reach 1,000 people | CPM = (Total campaign cost ÷ Total impressions) × 1,000 |
| Frequency | Average number of times a person in the target audience sees the ad during the campaign | GRP ÷ Reach % |
Roadstar is the audience measurement standard approved by the IOAA (Indian Outdoor Advertising Association) for India. It is developed and administered by MRUC (Media Research Users Council) and funded by IOAA members.
Roadstar measures OOH audiences through: (1) a comprehensive road and pedestrian traffic survey, (2) demographic profiling of audiences at key OOH sites, (3) a census of OOH inventory in covered markets.
Current coverage: Roadstar covers the major Indian metros. Tier 2 city coverage is expanding. The Indian Outdoor Survey (IOS), also funded by IOAA members, is building a fuller national census of OOH sites.
The IOAA Chairman (Times OOH CEO Shekhar Narayanaswami, 2026) has articulated the aspiration to move India from OTS-based buying to LTS-based measurement — aligning with the Geopath model in the US.
Geopath is the USA's non-profit OOH audience measurement body, established in partnership with OAAA. Geopath uses:
The Geopath methodology is the most rigorous available for OOH measurement globally. OAAA published an updated OpenOOH taxonomy in 2025–2026, enabling programmatic buyers to transact on Geopath audience data.
GRP is the universal currency of broadcast media planning. When OOH is expressed in GRP, it can be directly compared to TV and radio in the same plan. A TV campaign running at 300 GRP and an OOH component at 100 GRP together deliver 400 GRP (noting that OOH and TV audiences overlap).
OOH CPM is competitive with print and lower than TV for comparable reach in major metros — but the comparison is not direct because OOH impressions are passive (no opt-out), while digital and TV impressions can be skipped or blocked.
A media plan for an outdoor campaign should show: list of sites, location of each, DEC per site, total OTS, GRP, reach and frequency estimates, CPM, and total cost. If the plan shows only site names and rates without DEC or OTS, push back — you are buying on faith, not data.