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Scroll through the contacts in your phone. Hundreds of names. Now count the people you could call at 2 a.m. if something went badly wrong.
For most of us, the second number is tiny. Three, four, five. And that gap, between the long list and the short one, is what a British scientist spent his career trying to explain.
His name is Robin Dunbar, and the number he is famous for is 150. It gets quoted everywhere: in business books, in articles about social media, in talks about why you feel lonely in a crowd. But the 150 is only half the story. The more useful part is what sits inside it, and the honest part is how shaky the number itself turns out to be.
What Is Dunbar’s Number? The Short Answer
Dunbar’s number is the idea that a person can keep up roughly 150 stable relationships at one time. “Stable” here means people you know as individuals, people you could walk up to in a market and start talking with, and who would not be surprised to see you. Not best friends. Not strangers. The people in the middle.
Dunbar’s own test for it is simple: if you bumped into this person at a bar at 3 a.m. in an airport far from home, would you sit down with them for a drink without it being awkward? If yes, they are in your 150.
The number comes from a 1992 paper by Dunbar, then at University College London, in the Journal of Human Evolution. His actual estimate was 147.8. Everyone rounded it to 150, and the round number stuck.
Where the Number Came From (It Wasn’t About Friends)
Here is the first thing most summaries skip. The 1992 paper was not a study of human friendship. It was a study of monkeys and apes.
Dunbar looked at 38 kinds of primate and compared two things: how big their social groups were, and how big the “thinking” outer layer of their brain, the neocortex, was compared with the rest of it. The two went together. Bigger neocortex, bigger group. He drew a line through the data, then asked where a human brain would land on that line.
The answer was 147.8. But the paper also gave a range, and the range was wide: somewhere from about 100 to about 230. That caveat was there from the start. It just never made it into the business books.
There was a second part of the argument that is even more interesting. Monkeys hold their groups together by grooming each other, picking through fur for hours a day. Dunbar worked out that a group of 150 would have to spend around 42% of its waking time grooming to stay bonded, which is more than any animal can afford. His suggestion was that humans found a cheaper way to do the same job. We talk. Gossip, in his view, is grooming with words.
So the famous number was never really a limit on friends. It was a guess about brain size, and a theory about why we chat.
The Layers Inside the 150: 5, 15, 50, 150
This is the part that actually helps in real life.
When Dunbar and others started looking at real human networks instead of monkey troops, the 150 turned out to have a structure. It is not one flat circle. It is a set of rings, one inside the other, and each ring is about three times bigger than the one before it.
- About 5: the people you would turn to in a crisis. Dunbar calls this the support clique. Often a partner, a parent, a sibling, one or two friends.
- About 15: the sympathy group. Close friends. The people whose death would truly knock you sideways. You see most of them at least once a month.
- About 50: good friends. The people you would invite to a big birthday or a wedding.
- About 150: the whole active network. Everyone you know as a person and keep in some kind of touch with.
The rings keep going outward, with the same roughly-times-three pattern. Around 500 acquaintances. Around 1,500 faces you could put a name to. But the real relationships live in the inner four.
One of the nicest tests of this was a 2003 study by Russell Hill and Dunbar that looked at something very ordinary: Christmas cards. They asked 43 British households to keep track of every card they sent, close to 3,000 cards in all, and who lived in each house they went to. The total number of people reached by one household’s cards averaged 153.5. The number had been predicted from monkey brains. It showed up on a kitchen table in December.
The layers matter because they are a budget, not a ranking. Each ring inward costs more time. The inner five take the biggest share of your social hours by a wide margin. That is why you cannot simply decide to have 40 close friends. There are not enough hours in a week to keep 40 people in a ring that needs that much contact.
Is Dunbar’s Number Even Real?
Here is the caveat you deserve, because a lot of articles leave it out.
In 2021, three researchers at Stockholm University, Patrik Lindenfors, Andreas Wartel and Johan Lind, published a paper in Biology Letters with the blunt title “Dunbar’s number deconstructed.” They reran Dunbar’s basic method with more primate data and newer statistical tools. Depending on the method, their average estimates for humans came out well below 150. And the uncertainty was enormous. In one analysis the plausible range for a human group ran from 4 to 520 people. In another, from 2 to 336. Their conclusion was that picking any single number from this kind of brain data is pointless.
Dunbar disputed their methods, and the argument is still going. So where does that leave you?
A fair reading is this. The exact number 150 rests on shaky ground, and it was never precise even in the original paper. But the layered shape, the small ring inside the bigger ring inside the bigger one, has been seen again and again in real human networks: in card lists, phone records, and surveys. You can doubt the 150 and still find the rings useful. Most people, when they count honestly, do.
What the Rings Are Good For
The number is not a rule to obey. It is a mirror. Hold it up and a few things get clearer.
Online contact does not change the rings. You can have 2,000 followers and still have an empty inner five. The outer rings got easy to fill. The inner rings got no cheaper. If you have ever felt oddly alone after a day full of messages, that gap is why, and we went deeper into it in why you can feel disconnected from everyone while talking to people all day. If you want a quick, honest read on where you stand right now, our free How Lonely Am I? quiz takes a few minutes.
Time moves people inward. Nothing else does. Dunbar’s later work on friendship keeps landing on the same thing: the ring someone sits in is set mostly by how many hours you spend together. Not shared history, not good intentions. Hours. Which means a friend who drifts outward is usually not a friend who stopped caring. It is a friend you stopped seeing.
Someone moving in means someone else moves out. A new partner, a new baby, a new job that eats your evenings: each one quietly pushes a few people one ring outward. That is not a failure. It is arithmetic. It helps to know it is happening so you can choose who it happens to.
If you want to do one practical thing with all this, try it today, free:
- Write your five. Not who should be there. Who actually is. Who would you call at 2 a.m.?
- Write your fifteen. Then look for a name you expected in the five and found here instead. That is usually someone you miss.
- Move one person one ring inward. Not by messaging. By time. A walk, a meal, a call with no agenda.
The Oldest Example of the Rings Is Not in a Lab
There is a figure in history whom almost everyone, religious or not, associates with loving everybody. Crowds followed him. He fed thousands. He told a story about a shepherd leaving ninety-nine sheep to find one.
And yet, if you read the accounts of Jesus’ life with Dunbar’s rings in your head, something stands out. He built his life in layers too.
There were three he took with him into the hardest and strangest moments, the ones nobody else was invited into. There were twelve he lived with, travelled with, and ate with every day for years. There was a wider group of about seventy he trusted enough to send out ahead of him in pairs. After his death, about a hundred and twenty of his followers gathered in one room. And an early letter mentions more than five hundred people who saw him at the same time.
Three, twelve, seventy, a hundred and twenty, five hundred. The numbers do not line up exactly with five, fifteen, fifty and a hundred and fifty, and it would be dishonest to pretend they do. But the shape is the same: a very small circle, then a bigger one, then bigger again, each ring a little wider and a little less close.
The person most famous for loving everyone did not try to be equally close to everyone. He gave his deepest hours to a handful. Which raises a quiet possibility about your own tiny list of 2 a.m. names. Maybe it is not a flaw in you. Maybe it is how a human being was designed to love: a few people deeply, and everyone else through them. A southern African word for this idea, ubuntu, says a person becomes a person through other people. Not through all of them at once. Through the ones close enough to touch.
A good place to start: The Beginner’s Guide to Feeling God’s Presence Every Day. A simple way to notice you are never actually alone, even on the days your inner five feels thin. Get the free guide. Free.
You Were Never Meant to Hold Everyone
So, what is Dunbar’s number? A rough guess, drawn from monkey brains in 1992, that has been argued over ever since. Hold the 150 loosely.
Hold the rings tightly. They explain why the long list in your phone does not fix the short one, why friends drift when the hours stop, and why a small circle is not a small life.
You do not need 150 friends. You need five who know the real version of you, and the time to keep it that way. Start there. One person, one ring inward, this week.
Discussion Question
Do you think Dunbar’s number still holds in a world of group chats and followers, or has the internet genuinely changed how many people we can really know? Tell us what you think in the comments.
Share This
Dunbar’s number (150 friends) was never about friends. It came from a 1992 study of monkey brains, and the man who found it also said it was a range from about 100 to 230. The layers inside it are the useful part: https://bgodinspired.com/?p=117619
I counted my “2 a.m. people” after reading this. Five. Turns out that’s not a flaw, it’s the design. https://bgodinspired.com/?p=117619
A 2003 study predicted the size of your social world from brain size, then checked it against Christmas card lists. The cards came out at 153.5. Wild. https://bgodinspired.com/?p=117619
Questions People Ask About Dunbar’s Number
What is Dunbar’s number in simple terms?
Dunbar’s number is the idea that one person can maintain about 150 stable relationships at a time. The figure comes from a 1992 paper by the British anthropologist Robin Dunbar, who compared brain size and group size across 38 kinds of primate and estimated where humans would fall on that line. His estimate was 147.8, usually rounded to 150, with a range from about 100 to 230.
What are the layers of Dunbar’s number?
Dunbar’s number is made up of nested layers that grow by a factor of roughly three: about 5 people in the innermost support group, about 15 close friends, about 50 good friends, and about 150 in the full active network. Beyond that sit roughly 500 acquaintances and about 1,500 people whose faces you can put a name to. Each layer closer to the centre takes more time to maintain.
Is Dunbar’s number scientifically proven?
Dunbar’s number is disputed. A 2021 study by Patrik Lindenfors, Andreas Wartel and Johan Lind at Stockholm University, published in Biology Letters, reran Dunbar’s method with more data and newer statistics and found the plausible range for human group size was far too wide to support any single number, running from 4 to 520 people in one analysis. Robin Dunbar disagreed with their methods. The exact figure of 150 is uncertain, but the layered structure of 5, 15, 50 and 150 has been observed repeatedly in real human social networks.
Does social media change Dunbar’s number?
Social media does not appear to change the inner layers of Dunbar’s number. People can have thousands of online contacts, but the number of close relationships they keep stays small, because close relationships are limited by the time it takes to maintain them, not by how many people a person can reach. Online tools make the outer layers of acquaintances easier to fill while leaving the inner circle of about 5 and 15 people the same size.
How do you use Dunbar’s number in real life?
A practical way to use Dunbar’s number is to write down your innermost 5 people and your closest 15, then notice who you expected to be closer than they are. Because the layer a person sits in depends mostly on time spent together, moving someone inward means giving them hours, such as a shared meal, a walk or a call, rather than more messages. It also helps to accept that when a new person enters your inner circle, someone else usually moves one layer outward.
