Dunbar's Number illustration
Psychology / Anthropology / Social
Psychology / Anthropology / Social

Dunbar's Number

Our brains can sustain only so many real relationships.

Popularity
Usefulness
Aliases
Rule of 150 / the 150 law / social-brain limit
Domains
Evolutionary psychology, anthropology, social networks, organizational design

Definition

  • Dunbar's Number is the proposed cognitive limit — roughly 150 — to the number of stable, meaningful relationships a person can maintain.

Core Idea

  • Our brains can sustain only so many real relationships.
  • Around 150 is the suggested ceiling for a stable social group.
  • Closeness has a natural headcount, with smaller inner circles nested inside.

How It Works

  • Maintaining relationships requires cognitive and time resources.
  • Beyond a threshold, relationships become shallow or break down.
  • Groups larger than the limit tend to need formal rules and hierarchy to hold together.

Usage Example

  • A company growing past about 150 people often finds that informal coordination breaks down and needs explicit structure and process to function.

Famous Example

  • Example: Robin Dunbar's correlation between primate neocortex size and group size, extrapolated to humans as ~150.
  • Why it fits this rule: It sets an evolutionary ceiling on stable group size.
  • Verification status: Influential and widely cited, but the precise number and its strict interpretation are debated among researchers.

Use Cases / Situations Where It Applies

  • Designing team and unit sizes.
  • Understanding community and network limits.
  • Social media and relationship management.

When Not to Use or Common Misuse

  • Do not treat 150 as an exact, universal hard limit.
  • Do not ignore that weak ties beyond the circle still matter.
  • Do not use it to dismiss large-scale organization, which uses structure to scale.

Rule Invention / Origin

  • Invented by: Robin Dunbar.
  • Year of invention: 1990s.
  • Country / context of origin: United Kingdom evolutionary anthropology.

Evidence / Research Basis

  • Based on comparative primate data and human group observations; debated, with some studies questioning a single fixed value.