I’ve seen things.
I’ve seen the grimy sweat dripping off a brow as the speaker punishes three hundred slides in a half hour. I’ve seen the off-the-cuff confidence of a speaker give her talk without even using a single slide. I’ve seen a friend eat three Kentucky Fried Chicken Double Down™ sandwiches. I’ve seen things, man.
People keep focusing on this weird metric. They always ask me “well how many slides do you have left?” It’s an irrelevant question, though, because the number of slides you should plan for ultimately depends on the type of talk you want to give and the type of person you are.
A good first step
You’ll understand yourself more as you give more talks. As you practice more and more, you start understanding how many slides you need in order to comfortably get your point across. If this is your first talk, that might be a bit difficult to judge, though.
Personally, I go a bit heavier on the slides than most people. Slides are the outline for me: I don’t put that many words on a slide, because I only need a little push in order for me to remember what I wanted to talk about. Since I only use one or two words per slide, I tend to flip through them a bit quicker than many other presenters. That ends up generating maybe a hundred slides or so for a thirty-minute talk, for me.
But that can change depending on the talk. If it’s less technical, if it’s more of a story, you can get by with only a couple slides (or no slides at all!) With a less-technical focus, you don’t need to put as much jargon on the screen, and that lets you play with the pace and tempo as you go.
There’s really no way to easily judge how quickly you’re going to go through slides. Sometimes I’ll find myself doing ten slides in twenty seconds, if I’m trying to convey a rushed, more intensive moment (possibly for humor-related purposes). Sometimes I’ll sit on a slide for five or ten minutes, if the slide warrants it.
When it comes to timing, it resides entirely on you: how fast your cadence is, how much you drift off-tangent, and so on. If you’re new to public speaking, the best thing you can do for yourself is to start practicing it before you even finish the entire slide deck, so you have a better handle on how much time you’ll need to devote on making more slides.