According to a U.S. Defense Department Study in 1974, the perfect length of a presentation is 17.4 minutes. Really, this is what the research found.

Don’t believe it.

Here is the only rule you need to follow when it comes to presentation length: Speak for as long as you need to, provided you are consistently interesting and memorable to the people in front of you.

I have personally seen Anthony Robbins hold the attention of a room filled with 5000 people from 10:00 AM until Midnight. And they crowd wanted more! And you and I have seen thousands of speakers who put everyone to sleep within two minutes because they were so deadly dull.
So a three minute speech can be too long if you are incredibly boring and a 12 hour speech can seem too short if you are interesting.

So your focus as a speaker has got to be on covering your key points in a consistently interesting way. If you do that, the length of your presentation will often take care of itself.

Of course there may be times when you are under strict time limitations. For example, you may be presenting at a financial conference where every company is given exactly 20 minutes. Or you may be granted precisely 15 minutes to make a sales pitch to the general manager of an auto dealership on why she should advertise on your TV station. In these cases, make sure you don’t speak longer than the arranged allotted time. And if you want to know how long your presentation is, you must say it out loud when you rehearse and then time it. If you read it silently to get a sense of your length, you will end up with a severely inaccurate sense of how long your presentation is because you can read much faster than you can speak.

In my experience, most mediocre presenters tend to fixate on length of a speech because they have a negative mindset. They want to get through the speech with minimum pain or damage; therefore they focus on how to make the presentation shorter, faster, leaner and more concise. This is a horrible and destructive mindset! Once you realize that presenting is an opportunity to help yourself, your company and your cause, you won’t have a bias towards being short; instead, you will have a permanent bias in favor of being interesting and memorable.

Many speakers make the mistake of conceptualizing their speech in terms of length. They think “I am giving a 30 minute new business pitch.” Or “”I am giving a 25 minute quarterly review.” This is the wrong way to think about your presentation. Length should be a secondary thought.
Making your points come across in an interesting, memorable way is what counts. Great Hollywood directors know this. James Cameron didn’t set out to make a 90 minute movie about the Titanic. Instead, he set out to make the best movie about the Titanic that he possibly could. The fact that it was 3 hours and 14 minutes long was irrelevant to him. He used as much time as he needed to tell his story about a boat and an iceberg. You need to have the same philosophy with your presentation even if there is no love story angle.

Of course it’s possible to go on and on and be too long. But I have never once heard in 45 years an audience member turn to someone and say “I really wish that presenter had NOT told those last interesting, memorable, and useful case studies that will help me make my business grow more effectively.” If someone thinks your presentation is too long, chances are you became boring. So attack the real problem: the boredom, not the length.