What Is Dunbar's Number?

Where does Dunbar's number come from?

In the early 1990s, Robin Dunbar, then a professor of evolutionary psychology at the University of Liverpool, was studying the relationship between brain size and social group size in primates. He noticed a strong correlation: species with larger neocortices — the part of the brain responsible for higher-order thinking — tended to live in larger social groups.

Dunbar extrapolated this relationship to humans. Based on the size of the human neocortex relative to other primates, he predicted that humans should naturally form stable social groups of approximately 150 people. He then tested this prediction against real-world data and found striking consistency.

The figure of 150 seems to represent the maximum number of individuals with whom we can maintain a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us. Putting it another way, it is the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar.

— Robin Dunbar, "How Many Friends Does One Person Need?" (2010)

• Hunter-gatherer societies: The average clan size across studied societies is 148.4 people
• Roman military: The basic unit of the Roman legion, the century, contained approximately 150 soldiers
• Neolithic farming villages: Archaeological evidence suggests typical village sizes of 150-200 people
• Modern companies: W.L. Gore & Associates (makers of Gore-Tex) famously caps each factory at 150 employees to maintain organizational cohesion
• Christmas card networks: Dunbar's own study of British Christmas card lists found an average of 153.5 recipients per household

The consistency across such different contexts — from prehistoric villages to modern companies — suggests that 150 reflects a genuine cognitive constraint rather than a cultural coincidence.

The layers of friendship: 5 / 15 / 50 / 150

Dunbar's most practically useful insight is not the outer number of 150 but the concentric layers within it. Your social network is not a flat list of equal relationships. It is structured in layers of decreasing intimacy, each roughly three times larger than the one inside it.

• The inner 5 (support clique): Your closest confidants — the people you would call in a genuine crisis at 3 AM. These are typically a partner, best friend, and closest family members. You invest the most emotional energy here
• The 15 (sympathy group): Close friends and family whose death would be devastating. You share personal information freely with this group and see them regularly
• The 50 (affinity group): Good friends you see socially and would invite to a private party. You know significant details about their lives and feel genuine warmth toward them
• The 150 (active network): All the people you maintain a meaningful relationship with — you know their name, how they relate to you, and could have a real conversation if you met unexpectedly

The time and emotional capital you invest in a relationship determines which layer it occupies. If you stop investing, the relationship migrates outward. A close friend you have not spoken to in two years is no longer in your inner 15 — they have drifted to your 50 or beyond, regardless of how close you once were.

— Robin Dunbar, "Friends: Understanding the Power of Our Most Important Relationships" (2021)

This layered structure has profound implications for how you manage your time. Research shows that people spend approximately 40% of their social time on their inner 5, 20% on the next 10 (reaching 15), and the remaining 40% spread across the outer layers. This is not a choice — it reflects the cognitive and emotional investment required to maintain closeness at each level.

Does social media change Dunbar's number?

One of the most common questions about Dunbar's number is whether digital technology has expanded our capacity for relationships. The short answer is no. Multiple studies have confirmed that while social media increases the number of people you are aware of, it does not increase the number of meaningful relationships you maintain.

A 2016 study by Dunbar himself, published in Royal Society Open Science, analyzed the social media networks of 3,375 Facebook users aged 18-65. The results were clear: despite having an average of 150 Facebook friends (coincidentally matching Dunbar's number), users reported an average of only 4.1 people they could rely on during an emotional crisis and 13.6 people they felt expressed genuine sympathy for them.

Social media certainly help to slow down the rate of decay in relationship quality that would normally occur over time. But they do not overcome the inherent cognitive constraints on the number of friends you can maintain. The bottleneck is not technology — it is the human brain.

— Robin Dunbar, Royal Society Open Science (2016)

This finding is actually liberating. It means you do not need to feel guilty about not maintaining 500 LinkedIn connections or staying close with everyone you have ever met. Your brain is designed for social wellness within these natural limits. The goal is not to expand beyond them but to invest wisely within them.

How to use Dunbar's number in practice

Understanding Dunbar's layers gives you a practical framework for managing your relationships. Instead of trying to stay close with everyone, you can allocate your social energy strategically.

• Identify your layers: Map your relationships to the 5/15/50/150 model. This alone often reveals surprising gaps — people you consider close who you have not contacted in months
• Protect your inner 5: These relationships deserve the most investment. Schedule regular one-on-one time and prioritize these connections above all others
• Maintain your 15: Weekly or bi-weekly contact keeps these relationships vibrant. A quick message, a shared article, or a brief call is enough
• Rotate your 50: You cannot maintain all 50 at the same intensity, but monthly touchpoints prevent drift. A relationship tracker helps you rotate attention across this group
• Accept the 150 limit: Not everyone can be a close friend, and that is fine. Focus your energy where it creates the most mutual value

The most common mistake people make with their social networks is treating all relationships equally. A 30-minute coffee with someone in your inner 5 is worth more than a dozen superficial interactions with casual acquaintances. Prioritize depth over breadth.

— Marisa Franco, "Platonic: How the Science of Attachment Can Help You Make — and Keep — Friends" (2022)

A personal CRM becomes especially valuable when you think in terms of Dunbar's layers. By tagging contacts by closeness level and setting appropriate reminder frequencies for each layer, you create a system that naturally reflects how human relationships actually work.

How Linkiva helps you manage Dunbar's layers

Linkiva lets you organize your contacts by relationship closeness — your inner circle, close friends, good friends, and wider network. Set different stay-in-touch frequencies for each layer so your inner 5 get weekly attention while your broader 50 get monthly nudges. See at a glance which relationships need investment right now.

Your data stays completely private with zero third-party tracking and no data sharing. Linkiva is designed to help you invest your limited social energy where it matters most — right in line with how your brain naturally works.