I get this question a lot:
I'm giving a 60 minute presentation. How many slides should I use? There is of course no right answer to this. In fact, it's the wrong question to ask.
Your slides should be driven by the content you want to present and by the way you want to do that. If you only have one point to talk about then, in certain circumstances, a single slide may be all you need. Or you may need a lot of slides if, say, you want to show that a topic is far more complex than it seems at first.
In general, if you follow the concept of one idea per slide then you will probably use more slides than a "normal" (i.e. bullet point-laden) presentation would. Is that a problem? Of course not. Slides don't cost anything any more - they're just a mouse click each.
My guess is that the past, when slides were actual slides and cost time and money to produce, is what is still behind that question. Indirectly, this is also one of the reasons for the bullet point hell we often have to sit through. Unconsciously, we still think
I can't just waste an entire slide for that one point. Why not? Slides are free!
If you insist on numbers, here are some examples:
For a recent 30 minute presentation, I used 50 slides (which caused some raised eyebrows in my employer's marketing department). The point of the presentation was to show that the topic required much more attention to detail than you would expect at first, so a lot of those slides just pointed out these details. I didn't present a solution to most of them, I just wanted to raise awareness, so I could breeze through most slides in a short amount of time. I was fully aware that the audience wouldn't remember most of those details - that wasn't the point. I just wanted to show that there are a lot of details. I did slow down for the important points of course.
In my 2-hour Presenting for Geeks workshop, I'm using 70 slides. In a workshop, the learning aspect is at the centre of everything, so of course the pace is much slower.
A well-known presenter in the software development world usually goes through more than 500 slides during a 90 minute presentation. The record so far, if I remember correctly, is 715 slides - that's almost 8 per minute. This is of course a bit on the extreme end of the spectrum, but it does work for this particular speaker (though certainly not for everybody).
So, to repeat:
How many slides? -
It depends. Use as many or as few as you need. It depends on a variety of factors: Your topic, your point, and of course your audience.
People are often disappointed by these arguments - they expect that there's some magic formula that they need to stick to to make a good presentation. There isn't.
(Photo: "Just let it slide" by SqueakyMarmot, from Flickr)
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