How long should I talk for?

The traditional view of timekeeping is to organise your talk around no more than one slide every two minutes. Fine, but sometimes I talk about a slide for ages and sometimes I put an image for effect and it’s gone in a couple of seconds because it’s done its job.
At a University where I used to work, our lecture slots were organised in two hour slots: a colleague used to love very complex overhead projector slides. We devised a unit of measurement and named it after him. A “1 ****er” slide was a slide he could talk about for an hour: the ultimate was a “2 ****er” slide was the ultimate: he could do a whole 2 hour session from one slide.
When I left that University, I found myself competing for my new job with another colleague. I knew him to be a “One slide a minute” bulleted list man. True to form, he turned up to present to the staff in the new department with lots of slides printed out for all attendees. He dealt out the remnants of a shredded rainforest to the listeners as they all received their personal pile of paper.
I followed him. I had two slides. The first I put up at the beginning of the talk with the question on it that I had been asked to talk about. The other slide was displayed 18 minutes later and contained three key messages from the talk.Hmm, whom do you think got the job?

It is certainly true that many people from the bulleted list slide school of presenting simply have too many slides. In such cases, a simple rule of thumb may be helpful. However, a rule of thumb that might be more useful is
“People generally prepare too much material, so when you have prepared your talk, throw away 20% to keep to time”

The one thing that works against this rule is people’s tendency when nervous to speak more quickly.. So for example you may have practised your talk and timed it at 25 minutes, but then deliver it in 19 when anxious in front of your listeners. I remember watching in astonishment when one of my students managed to gabble through a talk that we had timed at 20 minutes the day before in under 10!
However, having too much material is not the answer. Your listeners will feel that they have been dragged along behind an express train: it really is better to correct the underlying problems, too much material and speaking too quickly rather than try and let one compensate for the other.
For more experienced talkers, my First Law of the length of a verbal piece of string states:
“You probably want to talk longer than they want to listen”

The second law states
“If the first law is wrong, then if you say too little, they will leave wanting more.”

So what can we replace the “2 minutes a slide” rule with? Well first of all, if you accept that the slides are not the talk, but are there to support the talk, then, the length of the talk is no longer directly measurable in terms of the number of slides, or vice versa. The talk should be:
1. No longer than it needs to be
2. No longer than you are allocated

Think about the last time you gave a talk.

  • Was it too long, too short, or just right?
  • How do you know?
  • Was there anyone listening, who you can ask to confirm your assessment?