The Dunbar Number as a Limit to Group Sizes

The chasm that starts somewhere between 9 to 12 people can be especially daunting for a small business. As you grow past 12 or so employees, you must start specializing and having departments and direct reports; however, you are not quite large enough for this to be efficient, and thus much employee time that you put toward management tasks is wast... See more

Dunbar's work itself suggests that a community size of 150 will not be a mean for a community unless it is highly incentivized to remain together.

At 5 to 8 people, you can have a meeting where everyone can speak out about what the entire group is doing, and everyone feels highly empowered. However, at 9 to 12 people this begins to break down -- not enough "attention" is given to everyone and meetings risk becoming either too noisy, too boring, too long, or some combination thereof.

This all leads me to hypothesize that the optimal size for active group members for creative and technical groups -- as opposed to exclusively survival-oriented groups, such as villages -- hovers somewhere between 25-80, but is best around 45-50. Anything more than this and the group has to spend too much time "grooming" to keep group cohesion, rat... See more

Dunbar is an anthropologist at the University College of London, who wrote a paper on Co-Evolution Of Neocortex Size, Group Size And Language In Humans where he hypothesizes: " ... there is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, that this limit is a direct function of relative neoc... See more

Essentially, as we increase group sizes beyond 80, to 150, 200, or even 350-500, we typically do so by breaking larger groups down into smaller ones, and continually reducing community sizes down to the point where they can be understood and managed by people -- and so efficiency reasserts itself.

My anecdotal evidence generally seems to support the idea that group sizes will usually plateau at a number lower than 150 participants. This comes from 20 years of doing facilitation both on and offline, running several software companies, and running various forums at America Online. In particular, many online communities provide good evidence fo... See more