Hong Life CalculatorsUnderstanding the outdoor advertising CPM calculator — concept and principle
Out-of-home (OOH) advertising covers billboards, bus shelters, transit wraps, station posters and screens in lifts or malls. Media owners often quote traffic counts, but not everyone who passes actually notices the ad. This calculator turns campaign cost, daily traffic, a visibility share and campaign length into visible impressions, cost per thousand visible impressions (CPM) and cost per day, so you can compare OOH with other media.
How it is calculated
- Visible impressions = daily traffic × visibility share × days
- CPM = campaign cost ÷ visible impressions × 1,000
- Cost per day = campaign cost ÷ days
Daily traffic is the number of pedestrians or vehicle occupants passing the site per day. The visibility share is the percentage you estimate actually see the ad, given its size, angle, distance and clutter. Any currency works.
The principle
CPM, from the Latin "mille" for thousand, is the standard yardstick for comparing media of different sizes: it states the price of reaching 1,000 impressions. Raw traffic overstates OOH audiences because many passers-by never look. Audience measurement bodies such as Geopath in the United States therefore adjust traffic with visibility research to estimate people likely to see the ad. Applying a visibility share is a simple version of the same idea. An impression is counted per pass, so one commuter passing daily for 28 days counts 28 times; impressions are not unique people.
Worked example
- Cost = $20,000, daily traffic = 50,000, visibility = 35%, days = 28.
- Visible impressions per day = 50,000 × 0.35 = 17,500.
- Visible impressions = 17,500 × 28 = 490,000.
- CPM = 20,000 ÷ 490,000 × 1,000 = $40.82.
- Cost per day = 20,000 ÷ 28 = $714.29.
How to read the result
A lower CPM means cheaper reach. Compare it with the CPM of other channels, but only on a like-for-like basis: an outdoor visible impression and a digital ad impression differ in attention, targeting and frequency. Test the visibility share: at 50% the CPM here would drop to about $28.57, at 20% it would rise to about $71.43. Because the estimate is so sensitive to this input, ask the media owner how their audience figures were measured.
Common mistakes
- Using raw traffic counts as if every passer-by sees the ad.
- Treating impressions as unique people reached.
- Leaving production, printing or installation costs out of campaign cost.
- Comparing a daily traffic figure with a weekly or monthly campaign cost period.
Frequently asked questions
What is a good OOH CPM?
It varies widely by city, format and site. Compare quotes for similar formats in the same market, measured the same way.
Is CPM the same as cost per person reached?
No. CPM counts impressions, which include repeat exposures. Cost per unique person reached is higher.
How do I estimate the visibility share?
Use the media owner's audited audience data where available. Otherwise consider viewing distance, angle, obstructions, illumination and the number of competing signs.
Sources: Geopath, out-of-home audience measurement (United States)