Dunbar’s number — the law of 150

Esther Sugihto
Aug 23, 2016 · 4 min read
The TV show Neighbours features 6 households across 22–32 Ramsay Street — approximately 24–30 people.

New York author, Malcolm Gladwell’s famous book, The Tipping Point, has an interesting story about the company Gore-Tex’s management structure. Through trial and error, they have devised a model of office design, whereby if the office grows to exceed 150 employees, they will start another office elsewhere until it hits 150 employees, and then start elsewhere again. Onwards it goes.

148 is the magical number called ‘Dunbar’s Number,’ oftentimes rounded up to 150. It is attributed to British evolutionary anthropologist Robin Dunbar, who has stated that 150 people is the ‘point beyond which members of any social group lose their ability to function effectively in social relationships.’

  • 5 intimate friends
  • 15 good friends (including the 5 intimate friends)
  • 50 friends (including the 5 intimate friends and 15 good friends)
  • 150 acquaintances (all-encompassing)

Of these, he says that we spend 60% of our time with our core groups of 50 friends, and 40% with the remaining 90 people. The number can be said to derive from our brain’s ability to maintain memories of 150 people, as well as the time necessary to devote to the group in order to keep relationships going.

What examples of this are there in history?

  • Neolithic farming communities are known to be around 150 people before it splits into a separate community
  • Roman military armies are approximately 150 soldiers in size; other modern armies are known to be typically 120–180
  • Average parish size for the Hutterites and Amish, denominations known for espousing communal living
  • Jury sizes are usually 12 people large
  • Coming back to Gore Tex, the work environment of 150 people results in everyone knowing each other’s name, no line-management systems or name badges, and everyone is committed to each other and the communal vision. It acts more like a lattice rather than a tree organisational structure, to quote Christopher Alexander.

While these might only be anecdotal examples, the bigger question I have is how does this relate to architecture? And in particular, housing?

  • Elemental’s Quinta Monroy housing development is for 100 dwellings, divided up into 5 clusters of 20 households each. Theoretically, 80 people per cluster, 400 people total.
Elemental’s Quinta Monroy housing in Iquique, Chile
  • Closer to home, Graeme Gunn’s Winter Park cluster housing proposal in Doncaster is for 20 households arranged in 4 lots of 5 houses each; so theoretically, 20 people per cluster; 80 people total.
Winter Park, Doncaster
  • More recently, the Nightingale housing model is capped at around 20–30 units, due in part with ability to fund such projects without being a sophisticated developer, but also to ensure that these buildings are “small enough that all living there will know each other and still having a connection to the street,” says Six Degrees architect James Legge. This results in a vertical community of 4–5 stories of about 60 people
  • Baugruppen projects (group housing developments driven by the owner occupiers) overseas have a ‘sweet spot’ of 15–30 households = approximately 60 people

Of course, Dunbar’s number can be said to wildly fluctuate from 100–200 people (self-professed by Dunbar himself). Furthermore, it has been said that the average Facebook user has 338 friends, well above Dunbar’s number, and users have not lived a full generation to determine the effects upon friendship formation, relationships and the social science behind it. We are able to electronically keep in touch with far more people beyond geographic location. Also, the original 150 people used to be the SAME 150 people, whereas now, our own Dunbar’s number of friends differ to the next person’s 150 friends.

I recently had a question from an Adelaide group starting up their own deliberative housing development — “what is the optimum size to begin the process of developing our cohousing project?” In my experience, something that keeps to approximately 50 people in total across the households (including kids); however a core group of no more than 12–15 people should make up the decision making committee. Why limit this number? Firstly, it allows enough diversity in the group to demonstrate a wider cross section of the community; and secondly, it is small enough to ensure decisions get made and do not drag out.

What are your experiences around designing architectural projects for a group of people? Please comment below to add your insights.

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Esther Sugihto

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Social Design + Architecture | curating community through architecture | Melbourne Australia | http://www.so-da.com.au