See also: How To Present a Course Project
From "How to Time a Presentation" by Lisa B. Marshall, June 5, 2009
In the past if you asked a presentation skills “pundit” you were likely to hear “one slide per minute,” but times are changing and I don’t think the answer is as simple as a certain number of slides per minute.
Again, it depends. It depends on the complexity of the content. It depends on if the slides are heavy in graphics or text. It depends if the slides use many progressive builds; it depends on how the builds are created. I’ve seen successful, dynamic 30-minute presentations that have used as few as 10 slides and as many as 150 sides. (Actually, I’ve also seen presentations with no slides that were great too, but you’re asking about presentations with slides.)
Complexity Needs to Be Considered
What is important to consider is the complexity of the ideas being presented.
In general, you should be able to talk for at least 30 seconds per slide. If you don’t have at least 30 seconds of content then you might consider combining the idea with another slide; or maybe use it as part of a progressive build.
For example, you may have a photo with one element highlighted; then you click to the next slide which is the same photo, except with a different element highlighted, and so on. Although you are using different slides, you are building progressively through a single main idea or, in this case, a single photo. However, again, if you’re not using a build then less than 30 seconds per slide may feel like you’re skipping something or glossing over details.
For complex ideas (or text heavy slides), for sure you’ll need more than a minute of discussion. Typically technical speakers should spend 1.5 to 3.0 minutes per slide presenting a single main idea. But, if it takes longer than say 3.5 minutes to present a slide (or one idea), then you likely need to add another slide. You could do it as a build or maybe you just break it up into two separate ideas.
So, the bottom line is that I think you should ignore all “slide per minute” rules you may have heard and instead use as many slides as you need to clearly and efficiently communicate your ideas.
I do understand, however, that this advice doesn’t help you to figure out how much material you need to prepare --which I think is the reason that most people ask this question to begin with.
So, I have a different heuristic for that.
Calculate Time Per Idea
I suggest taking your overall amount of time for the presentation, and then subtracting approximately 15% for the opening and closing. Then take the remaining time and divide it by the number of main ideas you’d like to present. The result will tell you how much time you have to present each main idea within the body of your talk.
So for example, if you are planning a 10-minute conference talk and you have 4 main ideas, you’ll have about 2 minutes per main idea. Which means you’re likely to have 4 or 5 slides for your main ideas (again depending on the content and the number of builds) and perhaps 3-5 slides for the beginning and ending portions. This means you’d end up with between 7-10 slides for a 10-minute presentation.
Let’s say you have a longer presentation, say 35 minutes. Again, subtract 15% for the “beginning and end”, which leaves about 30 minutes. Divide that by 4 (or 3 or 5 depending on how main ideas or main sections you’ve got). For this example, you’d end up with about 7.5 minutes per main idea.
Calculate Time Per Sub Point
With longer talks, the next step is to determine how many sub points you have to present per main idea and divide that into the time you have available for each main idea. So if you have 3 subpoints for the first main idea then you’ll have about 2.5 minutes per subpoint (probably 1 or 2 slides for each point). Of course, you’ll need to do the calculation for each main point that you have.
Calculate Your Flash, Fast, and Descriptive Slides
I sometimes use a quick and dirty method to calculate the timing. I categorize each of the slides into “flash”, “fast”, or “descriptive”. Flash slides take about 30 seconds to deliver, fast slides take about a minute, and descriptive slides about 3 minutes. Then, using these rough estimates, I can calculate how long it should take to make the presentation.
However, the only way to know for sure if I’ve have prepared the correct amount of material is deliver the presentation. That means practice with a timer.
However, I’ve noticed that some people run through the slides more quickly when they practice, others more slowly. I call this the n-factor (that is the impact of your nervous energy on the delivery of the presentation). Always take into consideration the impact of your personal n-factor by either adding or subtracting time.
Use Timing Check Points
Finally, and perhaps most importantly, to ensure that you don’t go over your time, calculate three timing check points within your presentation. For example in a 30-minute talk you should know exactly what needs to have been covered at ten minutes into the talk, at 15, and 25 minutes into the talk.
That way you can adjust your pace as your are moving through the materials. If you are behind at ten minutes, you know that you’ll need to start cutting some of the “nice to know” material as you move forward; then at 15 minutes, you check again. If you are now ahead, you can slow down and take more time to discuss or take questions from audience. The idea is to use the “timing” points to guide you along the way.
I use this technique for every talk and it works well. Just before I deliver a talk I prepare a piece of paper with my “timings.” I start with the time I want to finish (always 8-10 minutes before the “next speaker” deadline so there is time for questions). Then I add a few minutes to the start time, because most groups don’t get started exactly on time.
Then, on a small piece of paper, I calculate the exact time on the clock that represents my timing points. So, for example, I write 9:13 for my first check point, 9:18 for the second check, and 9:28 as the last check. Remember, I’m in my upper 40’s so I always keep a clock with a very large dial next to my laptop. That way I can easily check the time and where I should be within the presentation itself.
Double Check Your Math
One small warning though: double check, maybe even triple check your timings! Once I accidentally calculated the points incorrectly and didn’t realize it until I was about a 2/3 of the way through the presentation! Once I realized I had done it wrong, I had to cut a lot of material from the end of the presentation. I didn’t go over my time, but the presentation certainly wasn’t as good as it could have been.
So there you have it, several techniques to help you determine how many slides to create and more importantly techniques to ensure that you successfully time your presentation and don’t go over your time limit.