How many slides for a 10, 20 or 45-minute talk?

You’ve been given twenty minutes, and the first question that comes to mind is: how many slides? The honest answer fits in one sentence. The number of slides tells you almost nothing about how long a talk will run, because a slide can stay on screen for ten seconds or for four minutes.

What takes time is the ideas. Here’s how to count them, along with a few benchmarks to make sure you’re in the right ballpark.

Why “one slide per minute” doesn’t work

The rule gets repeated everywhere, and it has one flaw: it treats every slide the same way. But a presentation mixes very different kinds of slides.

• A section title slide goes by in five seconds.
• A big statement or a key number needs fifteen to thirty seconds: time to say it and let it sink in.
• A diagram you walk through, a table or a demo can hold the screen for three or four minutes.

Twenty slides of the first kind fit into five minutes. Twenty of the last kind take sixty. Counting slides is like judging the length of a text by its page count without checking the font size.

Count your ideas

By “idea,” we mean something you want the room to remember and be able to repeat. To land it properly, you need to introduce it, explain it, give an example or some evidence, then wrap it up. Allow two to three minutes per idea. It’s a rough estimate, but it holds steady from one topic to the next.

The math then becomes simple:

• 5 minutes: one idea, two at the very most.
• 10 minutes: three ideas.
• 20 minutes: five to seven ideas.
• 45 minutes: ten to twelve ideas, grouped into three parts.

Always set aside time for the opening, the conclusion and questions. In a twenty-minute slot, that leaves you fifteen for the substance.

A few benchmarks anyway

Once you’ve counted your ideas, the number of slides follows. For a typical presentation, with a few quick slides and a few you talk through, you’ll usually land in these ranges:

• 5 minutes: 4 to 6 slides.
• 10 minutes: 7 to 10 slides.
• 20 minutes: 12 to 18 slides.
• 45 minutes: 25 to 35 slides.

If you’re well above that, there are two possible explanations. Either your slides are light and move quickly, and you’re fine. Or you have too much to say, and no layout will save you.

Guy Kawasaki, who has listened to hundreds of pitches from entrepreneurs, boiled his advice down to three numbers: ten slides, twenty minutes, thirty-point type. His rule is meant for pitching investors, but its spirit applies everywhere: few slides, time to talk, and text big enough that you can’t cram in too much.

The only reliable measure: rehearse out loud

We read in our heads twice as fast as we speak. Running through a talk silently always takes less time than giving it for real. In front of an audience, people speak at around 130 to 160 words per minute, pauses included.

So rehearse out loud, standing up if you can, with a timer running. Note the time at the end of each section, not just at the very end. That way you’ll know where you’re dragging.

Tip If you write speaker notes for each slide, count their words: 300 words is roughly two minutes of talking.

Finally, expect everything to take longer on the day: a question, a cable, a latecomer. A talk rehearsed at eighteen minutes fits in a twenty-minute slot. A talk rehearsed at twenty minutes runs over.

Too long? What to cut first

When the timer says it’s too long, the temptation is to talk faster. That’s the worst fix: the room tunes out, and so do you. Cut instead, in this order.

1. The background everyone already knows. The project history, the team introductions, the recap of the agenda.
2. The second example. One example sheds light; the next one just repeats it.
3. The methodology details. Save them for questions, or for an appendix slide you only bring up if someone asks for it.
4. An entire idea. It’s the hardest cut, and the most effective. Five ideas that land beat seven rushed ones.

Don’t cut the opening or the conclusion: they’re what the room remembers best.

In short

The right number of slides is the one that gives each idea its two to three minutes. Count the ideas, work out the slides from there, then rehearse out loud with a timer. And if you’re torn between two versions, pick the shorter one: no one has ever complained that a presentation ended early.

Next, find out how to build your outline starting from the conclusion.