This is another tough question to give a definitive answer to. How long is a piece of string?
The length of your presentation should always be determined by timing, and not by the number of slides. If you have an open-ended slot to deliver your presentation (not including Q&A), we recommend that you make your presentation twenty minutes long in order to make the most of audience attention spans.
While the time it takes to present a slide can completely vary depending on content, presenter, and even audience participation, a safe rule to follow when estimating how many slides your presentation will entail is to estimate a slide a minute. With title and value proposition slides included, we’d expect an average 20-minute presentation to have around 25 slides most of the time. But in reality, this varies greatly – and length of presentation on its own should never be used to calculate slide number.
Really, it depends on how many slides it will take to effectively get your content across. You shouldn’t even be thinking in terms of slides until you’ve identified your presentation objectives, message and structure. Once you have these outlined, you can start to think about how your information will be delivered visually, and this is what decides how many slides you will need. Even at Convinced, we can only provide rough estimates of how many slides we think a presentation will require. Sometimes visualisations require more stages than you’d expect; sometimes less. It really does vary.
So stop worrying so much about the number of slides, and focus your attention instead in getting your message across in the most effective way. The number of slides will follow naturally as you outline the structure of your presentation.