Dunbar's Number Calculator
Calculate the cognitive limit of stable social relationships based on the neocortex ratio regression.
Social Layers (Dunbar's Circles)
| Layer | Name | Size | Description |
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How to Use the Dunbar's Number Calculator
- Select a species preset — choose Human, Chimpanzee, Gorilla, or Macaque to auto-fill the neocortex ratio.
- Or enter a custom ratio — the neocortex ratio is the volume of the neocortex divided by the volume of the rest of the brain.
- Read the results — the maximum social group size and the breakdown into Dunbar's concentric social layers.
Understanding Dunbar's Number
In 1992, British anthropologist Robin Dunbar published a groundbreaking paper correlating primate brain size with social group size. By plotting the neocortex ratio against observed group sizes across primate species, he derived a regression equation that predicted humans should naturally form groups of approximately 150 individuals. This number has since been validated across diverse contexts — from Neolithic villages to Roman military units to modern corporate departments.
The Regression Equation
Dunbar's Number is calculated using a reduced major axis regression on primate data:
log(N) = 0.093 + 3.389 × log10(neocortex ratio)
The human neocortex ratio of approximately 4.1 produces a predicted group size of about 148, commonly rounded to 150. This represents the number of people with whom you can maintain a genuine social relationship — knowing who they are and how they relate to every other person you know.
The Social Brain Hypothesis
Dunbar's work builds on the social brain hypothesis: the idea that primate brains evolved primarily to handle the computational demands of complex social relationships, not ecological challenges like finding food or avoiding predators. Managing a social relationship requires tracking histories, predicting behavior, and understanding group dynamics — all computationally expensive tasks that scale with group size.
Dunbar's Concentric Circles
Beyond the famous 150 number, Dunbar identified a structured hierarchy of social circles, each approximately three times larger than the previous one. The innermost circle of about 5 people represents your closest friends — those you would call in a crisis. The 15-person sympathy group includes close friends you see regularly. The 50-person band represents your extended social circle, and the 150-person clan is your full active social network.
Evidence Across History
The ~150 number appears across human societies with remarkable consistency. Neolithic farming villages typically contained 150-200 people. The Roman legion was organized into centuries of ~80-100 soldiers. The Hutterite communities deliberately split when they reach 150 members. Gore-Tex (W.L. Gore & Associates) famously limits factory units to ~150 people. Modern military companies worldwide average ~130-150 soldiers. The consistency across cultures and centuries suggests a deep cognitive constraint.