Practitioner · Lesson 3 of 5
Brand safety and viewability
About 10 minutes · Yogender Kumar, Managing Partner
By the end of this lesson you'll be able to
- Explain the standard for a viewable impression
- Calculate the real cost of a viewable, valid impression
- Choose controls that keep ads on suitable pages
Why this matters
Paying for an impression doesn't mean anyone saw it. Some ads load below the fold, some are seen by bots, and some land next to content you'd never choose. Each of those changes what you're really paying.
The core idea
Three checks sit between an impression you pay for and one that's worth paying for.
Viewability. The industry standard, set by the Media Rating Council (MRC), counts a display ad as viewable when at least half its pixels are on screen for one continuous second. For video it's half the player for two continuous seconds. An ad that loads at the bottom of a page nobody scrolls is paid for but never seen.
Invalid traffic (IVT). Some impressions are served to bots (bot traffic) and automated scripts, not people. Some is simple to filter, such as known data-centre traffic. Some is designed to look human.
Brand safety and suitability. Safety means avoiding content no advertiser wants, such as hate speech or illegal material. Suitability is your own line: a family brand might avoid news about crime, while a news app might be fine with it.
Verification tools, such as Integral Ad Science or DoubleVerify, measure all three and can block bad impressions before you bid.
Worked example
Hollin & Co is an imaginary UK homeware brand, so the figures are illustrative. Its media trader compares two sources of the same audience.
Source A, open auction at a £3 CPM. Verification shows 45% of impressions are viewable and 10% are invalid.
Out of 1,000 impressions, 450 are viewable, and 90% of those are valid: 405. So each 1,000 viewable, valid impressions really costs £3 × 1,000 ÷ 405 = £7.41.
Source B, a private marketplace deal at a £4.50 CPM. 75% are viewable and 1% are invalid.
Out of 1,000 impressions, 750 are viewable, and 99% of those are valid: about 743. So each 1,000 viewable, valid impressions costs £4.50 × 1,000 ÷ 742.5 = £6.06.
This treats viewability and invalid traffic as separate filters. Your verification report will give the exact split.
Source A looks 33% cheaper on the rate card. Counted by impressions people could actually see, it's about 22% dearer.
My view: never compare CPMs without the viewability and invalid traffic rates next to them.
Rate card against the real cost of 1,000 impressions people could see
In practice
- Ask for viewability and invalid traffic rates by source, every month.
- Compare sources on cost per thousand viewable, valid impressions.
- Use an approved list of sites and apps, not only a block list.
- Write down your own suitability rules, and review them each quarter.
- Use pre-bid filtering, so you don't pay for impressions you'd reject.
- Check placement reports by hand, not only the verification summary.
Common mistakes
- Paying for impressions nobody could see. Low viewability can more than double the real price. Measure it by source.
- A block list on its own. New unsuitable sites appear every day. An approved list keeps you where you chose to be.
- Blocking too broadly. Banning every news keyword cuts off a lot of quality journalism. Set suitability rules that fit your brand.
Try it yourself
A source costs £2 per thousand impressions. 40% are viewable and 20% of those are invalid. Another costs £5 per thousand, with 80% viewable and 2% invalid. What's the cost per thousand viewable, valid impressions on each?
Show answer
First source: 1,000 × 40% × 80% = 320 viewable, valid impressions. £2 × 1,000 ÷ 320 = £6.25. Second source: 1,000 × 80% × 98% = 784. £5 × 1,000 ÷ 784 = £6.38. They're almost the same price. The first is slightly cheaper, but with a fifth of its viewable impressions invalid, I'd want to know where that traffic comes from.
Quick check
Not scored. Pick an answer to see the explanation.
When does a display ad count as viewable under the industry standard?
A source costs £4 per thousand, 50% is viewable and none is invalid. What's the cost per thousand viewable impressions?
Key takeaways
- An impression you pay for isn't always one anyone could see.
- Compare sources on cost per thousand viewable, valid impressions.
- Approved lists keep you on chosen sites. Block lists only remove known bad ones.
- Safety rules are shared. Suitability rules are yours to set.