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No. 124 · People · Sociology

Dunbar’s Number

We can keep up only about 150 real relationships at once.

Dunbar's number, proposed by anthropologist Robin Dunbar, suggests humans can maintain around 150 stable relationships, with smaller inner circles of about 15 close friends and 5 intimate ones. Past that, ties thin into acquaintances.

Use it to guard time for the people who matter most, and to design teams and communities that stay human-sized. Treat 150 as a rough guide rather than a law, since people vary widely.

In the Almanac

“Brains and group sizes”, 1992 · “W. L. Gore & Associates”, 1958

Both stories in full, three ways to use it and where it misleads.

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Dunbar's Number: The Cognitive Limit of Human Connections

Questions

What is Dunbar’s Number?

Dunbar's number, proposed by anthropologist Robin Dunbar, suggests humans can maintain around 150 stable relationships, with smaller inner circles of about 15 close friends and 5 intimate ones. Past that, ties thin into acquaintances.

How do you use Dunbar’s Number?

Use it to guard time for the people who matter most, and to design teams and communities that stay human-sized. Treat 150 as a rough guide rather than a law, since people vary widely.

When does Dunbar’s Number matter?

Dunbar’s Number is one of the 60 mental models for people, the situations where you ask: Why do people act as they do, and how do I work with them? Within that, it belongs to “How groups behave”, alongside Bystander Effect, Chilling Effect and Groupthink.

What is an example of Dunbar’s Number?

Two stories show it at work: Brains and group sizes (1992) and W. L. Gore & Associates (1958). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.

Which mental models are related to Dunbar’s Number?

Hierarchical Organisation, Network Effects and Mythical Man-Month. Dunbar’s Number itself comes from sociology.