An eye-tracking study of nearly 4,300 consumers by InSkin Media also reveals that viewable online ads receive 0.7 seconds for gaze time on average.
Research Now and Sticky says 25% of "viewable" ads are never looked at, while one-third are looked at for one second and 42% are viewed for more than a second – the median being 0.7 seconds.
To be looked at for one second, an ad needs to be viewable for 14 seconds, the study said.
An ad is deemed to be viewable if it meets industry guideless of 50% of it being on screen for at least one second.
The study also provides an insight into how long an ad needs to be viewable in the first place to hit certain levels of so-called "gaze time".
On average, to be looked at for up to a second an ad needs to be viewable for 14 seconds. Ads achieving at least one second of gaze time are viewable for an average of 26 seconds.
Meanwhile, for at least two seconds of gaze time, the average viewability is 33 seconds. For three or more seconds of gaze time, average viewability is 37 seconds.
Steve Doyle, InSkin Media’s chief commercial officer, said: "A campaign should be assessed in three stages: did the ad have the opportunity to be seen, was it actually looked at and what was the impact.
"It should be judged and optimised against the last stage (impact) but the focus on viewability means campaigns are increasingly optimised against the first stage (the opportunity) which can be counter-productive to maximising impact.
"Why? Smaller formats have higher ‘opportunity to be seen’ rates as their size means it’s easier to hit viewability thresholds – but gaze time is very low. Thus, it’s optimising on low engagement and low impact."