How long should a presentation be?
How to work out the right length for a presentation, how many slides and words fit in the time you have, and what to cut when you run long.
There is no single right length for a presentation. The right length is the time you were given, minus a margin, filled with only what your audience needs to make a decision or remember one idea.
What you can calculate is whether your talk fits. Here is how.
Start from the slot, not from the slides
If you have a 20-minute slot, plan a 16 to 18 minute talk. Talks almost always run longer live than in rehearsal: you pause for reactions, a slide takes a moment to load, someone laughs. A margin of 10 to 20 percent keeps you from rushing the ending, which is the part people remember.
If questions are part of the slot, decide up front how many minutes they get and plan the talk for what is left.
Words: how much you can say
Most people present comfortably at around 120 to 165 words per minute, with about 140 as a relaxed middle. That gives you a simple budget:
| Talk length | Words, at about 140 a minute |
|---|---|
| 5 minutes | about 700 |
| 10 minutes | about 1,400 |
| 15 minutes | about 2,100 |
| 20 minutes | about 2,800 |
If you wrote speaker notes, count their words and divide by 140. If the result is well above your time, your talk is too long, no matter how fast you plan to speak. Speaking faster to fit more in is the most common mistake: the audience follows less, not more.
Slides: how many fit
There is no fixed rule, because slides differ so much. A full-screen photo can take ten seconds; a chart people need to understand can take two minutes.
A practical way to check: give each slide a time budget based on what it has to do, then add the budgets up. Title and section slides get a few seconds. Slides with a key argument, a demo or data get the most. If the total is over your time, you know exactly which slides to shorten.
Signs your talk is too long
- You skip slides or say "I'll go quickly through this one".
- The last two or three slides get less than half their planned time.
- In rehearsal, you finish over time even when nothing goes wrong.
- You have more than one main message.
What to cut first
When you need to lose time, cut in this order:
- Repetition. Two slides that make the same point become one.
- Background the audience already knows. Every audience knows less than you, but rarely as little as you assume.
- Detail that belongs in a handout. Tables, methods and full numbers can go into an appendix or a follow-up email.
- Your second-best example. One strong example beats two good ones.
Never cut the ending or the ask. If people only remember one slide, it will be the last one.
Check it by rehearsing out loud
Estimates get you close, but only a spoken rehearsal tells you the real length. Time one full run, slide by slide, and compare it with your plan.
RehearseWise does this for you: when you upload your slides, it reads your speaker notes and slide text to suggest a length, gives each slide a time budget, and while you rehearse it shows how long each slide really took, so you know exactly where your minutes go.