Wordcount in banner ads
The average adult can read 200-250 words per minute. If you Google this topic you'll see a range of numbers; this is basically where they average out. Let's simplify and call it 225 words per minute.
For a 15-second banner ad placement, that works out to 56 words. Now, that's constant, uninterrupted reading; not waiting for words to appear, not looking at imagery or animation.
We also have to think about making the banner accessible for people who read less quickly than the average adult.
Based on all of that, my strong recommendation is no more than 25-30 words per banner ad.
(If you're in pharma like I am, of course that's not including ISI and end matter. However, it should include things like footnotes and references. Those are important parts of the banner content, and we need to make sure users are able to read them.)
(To take this idea a bit further: the ISI is probably auto-scrolling, and the user probably has the ability to grab the scroll bar and read it at whatever speed they want. Same for the end matter; it's inside the ISI area, so the user has control. The user cannot control the speed of all of the content in the body area of the banner, so it is our responsibility to make sure it's on screen for enough time for to be read, by users of varying reading levels.)
If we include more content than 25-30 words, many users simply won't be able to easily read the banner, and so they won't engage with it — and this means we haven't done our job. Remember, no user is willing to work hard to a read an ad. Make it difficult, and we've lost them.
If we're asking ourselves, "How much copy can we fit in these 15 seconds?" or "How do we want to tell our story?" we're probably not thinking about the banner ad with the most effective content strategy.
The banner's job should not be to educate the user. It should not tell them something, it should make them want to know something — so we can get that tap/click. We can do that with a lot fewer words than it would take to educate them about something. Remember, once the user is on your site, they'll have access to all of your content.
Fewer words in a banner ad also means we can make the text bigger, which is another big advantage. We want big, we want eye-catching. That's a big part of how we'll get users to engage.
For whatever it's worth, I truly believe that 10 huge words will always perform better than 30 small ones. Less is more! Direct, bold, provocative is better! We don't win anything when the user reads all the text in our banner. We win when they tap/click — so that must be our main focus.
– Manning
Questions/comments? Feel free to contact me at manning@manningkrull.com. I update these articles pretty frequently — best practices evolve over time as the world of digital quickly changes, and I always welcome insights from others.