Dunbar’s Number
Dunbar’s number shows that trust-based coordination has a ceiling, even if the exact number is contested.
What Is It?
Dunbar’s number is the proposed cognitive limit on how many people someone can maintain stable social relationships with, relationships where you know who each person is and how they relate to everyone else in the group.
British anthropologist Robin Dunbar derived the commonly cited figure of 150 by correlating neocortex size with typical group size across primate species, then extrapolating that relationship to humans. He also proposed the number isn’t really one number: it nests in layers of roughly 5 (closest support), 15 (close friends), 50 (a wider circle), and 150 (the outer edge of relationships you can meaningfully track), with looser bands of acquaintances beyond that.
Why Does It Matter?
W.L. Gore & Associates, the maker of Gore-Tex, built this directly into how it runs its plants. Founder Bill Gore capped every facility at 150 employees and 150 parking spaces. Once the lot filled, the company built a new plant next door rather than expanding the existing one. Past that size, he found, people stopped being able to track who everyone was and how they related to the rest of the plant, and the informal trust that let the company run without heavy bureaucracy started to break down.
What Changes Once You See It?
You stop treating group size as purely a resourcing question, headcount for headcount’s sake, and start asking whether a group has grown past the point where people can still hold the whole social map in their head.
You start noticing that once a group crosses that threshold, the informal trust that used to substitute for process usually gets replaced by process, whether or not anyone decided to add it. More meetings. More documentation. More formal approval chains. Not because people got worse at their jobs. Because nobody can track the whole network anymore.
Common Misunderstandings
- 150 is not a precise, scientifically settled number. A 2021 reanalysis of Dunbar’s original method, by Patrik Lindenfors, Andreas Wartel, and Johan Lind, found that the same data and methods produce estimates ranging from roughly 4 to over 500 people depending on the statistical approach, with confidence intervals wide enough that the authors concluded no single number could be reliably derived this way.
- It is not about how many people you can recognize or work alongside. It’s about how many relationships you can actively track: who someone is, how they relate to you, and how they relate to everyone else.
- It is not one number. Dunbar’s own model nests several layers of closeness, and most organizations don’t need everyone sitting at the same layer.
- It does not mean an organization must cap out at 150. It means something changes in how a group needs to coordinate once it grows past whatever its own threshold turns out to be.
Diagnostic Question
Has this group grown past the point where people can still hold the whole social map in their head, and if so, has anything been redesigned to compensate?
Explore Further
Field Notes
None yet. This concept is a strong candidate for a future Field Note built around the W.L. Gore parking lot story.
Origin
Robin Dunbar proposed the number in the early 1990s, based on research correlating neocortex size with group size across primate species. The 2021 statistical critique appeared in Biology Letters as “Dunbar’s number deconstructed.”