How many friends can you have?
The Dunbar number is actually a series of them. The best known, a hundred and fifty, is the number of people we call casual friends—the people, say, you’d invite to a large party. (In reality, it’s a range: a hundred at the low end and two hundred for the more social of us.) From there, through qualitative interviews coupled with analysis of experimental and survey data, Dunbar discovered that the number grows and decreases according to a precise formula, roughly a “rule of three.” The next step down, fifty, is the number of people we call close friends—perhaps the people you’d invite to a group dinner. You see them often, but not so much that you consider them to be true intimates. Then there’s the circle of fifteen: the friends that you can turn to for sympathy when you need it, the ones you can confide in about most things. The most intimate Dunbar number, five, is your close support group. These are your best friends (and often family members). On the flipside, groups can extend to five hundred, the acquaintance level, and to fifteen hundred, the absolute limit—the people for whom you can put a name to a face.