How long should a film be?

This came up on a science films mailing list the other day — how long should a web video be, and what evidence do we have? My response: sheesh. You’re joking, right?

  • It’s not about how long films should be, it’s about how long this film should be. It’ll vary for every film, and every format. One of the big advantages of the web over broadcast is not being stuck with fixed durations.

  • Evidence? You want evidence? That’s ridiculous. Or at least, it’s a research project, because the question boils down to: does video work as a communication tool? To which we know by inspection that that answer is: “yes, except when it’s no.” If you want solid evidence for how effectiveness correlates with duration, you’re going to be waiting for a long time. And you’d still only be looking at correlation.

  • How long for whom? Different audiences and different audience contexts have different needs. For whom are you making the film, and how and when do you expect them to watch it?

  • What are the trade-offs? A subject for another post, another time, but: it often takes more effort and skill to make a good three-minute film than it does to make a six-minute film on the same subject. If 100,000 people watch, that’s two-thirds of a person-year you’ve avoided wasting. But it might cost you twice as much to make. Where’s the balance for you and your audience?

  • What’s the purpose of the film? this comes back to audience context, but: is the film intended to provide a talking point you hope people might discuss at the office water-cooler or down the pub? Is it detailing a specific idea or technique of particular interest to the viewer? Is it to be watched in a professional context, providing a briefing on a specialist subject? For each of these situations, your audience makes different judgements about their acceptable level of investment.

  • If you do find some data about retention rates versus film duration, how does that control for some films being plain less good than others? When was the data captured — viewing habits are changing so quickly, it had better be more recently than, say, 18 months ago, or it’s irrelevant.

  • What’s your success metric? Audience reach? Recall?

Asking how long a film should be is exactly equivalent to asking how long a piece of writing should be. Sane answers come down to things like:

A film should be as long as it needs to be, and no longer.


Good films can sustain for longer than bad films.

…both of which are based on aesthetic judgements, not empirical evidence. And there’s the problem: if you try to reduce communication to hard numbers, you’re rather missing the point.

Obligatory marketing message: one of the things StoryCog does is work through this sort of issue with clients. We make films, and we do that consulting thing too.


StoryCog is a communication consultancy and film production company; see more about us here, or explore the links above left. The views expressed in this blog are those of the authors, though they're quite likely to represent the company's position too.


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