Viewability
Viewability is the share of ads that were actually on screen long enough to have a chance of being seen. An impression is one showing of the ad. The usual bar is half the ad on screen for one second, or two seconds for video. It is a chance to see, not proof anyone looked.
Theodor Lindfors, Founding Marketer ·
Formula
Viewability rate = viewable impressions / measured impressions
What counts as a viewable impression
Let's take a shoe workshop in Mexico as an example. They make leather shoes and sell them online to Mexico and the United States. The workshop buys display on sites like a running-news website that is free to read and makes money by selling ad space. A served impression only means the ad was requested. Viewability asks a narrower question: was enough of the shoe photo actually on the reader's screen, for long enough, to have a chance of being seen.
The MRC (Media Rating Council) standard: at least 50% of the ad's pixels in the viewport for at least one continuous second for display, and two continuous seconds for video. Large format ads use a lower pixel share because they cannot fit 50% on a small screen at once. Different vendors and platforms implement measurement differently, and some impressions cannot be measured at all. That is why measured impressions, not served impressions, belong in the denominator.
How to calculate a viewability rate
Divide viewable impressions by measured impressions. Let's take a shoe workshop in Mexico as an example. They make leather shoes and sell them online to Mexico and the United States. The workshop buys 1,000,000 served impressions. 800,000 of those 1,000,000 served impressions can be measured. 560,000 of those 800,000 measured impressions pass the threshold. Viewability is 560,000 / 800,000 = 70%. Always state the measurement rate alongside it. A 90% viewability rate on 30% measurement is not a number to celebrate. Most of the buy was never checked.
How to use viewability in buying
Compare viewability at the placement level, not the campaign level. Cheap inventory tends to be cheap because it sits below the fold on a running-news website, or in a sticky footer. When you pair viewability with cost, you get viewable CPM (cost per thousand viewable impressions), which is the honest price of a seen impression. A $4 CPM (cost per thousand impressions) at 50% viewability is an $8 viewable CPM.
A large gap between CPM (cost per thousand impressions) and viewable CPM (cost per thousand viewable impressions) points at the placement, not the bid. Raising bids on inventory nobody sees only raises the cost of not being seen. Let's take a shoe workshop in Mexico as an example. They make leather shoes and sell them online to Mexico and the United States. The workshop should cut the footer before it raises the homepage bid.
Common viewability mistakes
- Chasing 100% viewability. Some formats and environments structurally cannot reach it.
- Ignoring the measurement rate and comparing vendors that measure different amounts of a shoe workshop's buy.
- Treating viewability as an outcome metric. It is a hygiene check on inventory quality.
Lemonado
See this number in Lemonado
Lemonado reads spend and results together from the platforms you connect, so you can ask for this metric without building a sheet. It can also act on what it finds, inside rules you set.