When you're planning a podcast, whether for online learning purposes or entertainment, size does matter.

As stated elsewhere on this website, the human brain takes in information through three primary channels: through seeing, through hearing, and through touch/experience.

The brain is a mighty multitasking machine, and so when we learn, we tend to learn best when we engage all those channels.

A podcast, however, is processed solely through the brain's audio channel -- and that channel will become fatigued fairly quickly.

On average, when you produce audio material for education, your listeners will retain the knowledge best if your program is no more than 20 minutes in length. If your topic is large and complex, it's far better to break it into several 20-minute podcasts instead of producing one long show. That way, your listeners can take the information in in small doses, and rest their brains in between.

If you pay attention to commercial and public radio programming, you'll see this 20-minute model in action. Most radio programs, even when they're an hour or more in length, will break the hour up into several shorter subjects. Or, if the whole hour is about one topic, the show will be broken up into shorter segments with breaks in between.

Not to mention, when you're keeping to a 20-minute format, it forces you to keep everything about your show succinct, relevant, and purposeful. (You only have 20 minutes, after all!) And this results in a high-quality podcast.