We made mocking reference recently to 120 being the average number of friends people have on Facebook. However, anthropologist Robin Dunbar suggests that most people have an average of 150 friends (leaving aside their status as online acquaintances or otherwise). He told BBC News:
They usually consist of an inner circle of five "core" people and an additional layer of 10, he says. That makes 15 people - some will probably be family members - who are your central group and then outside that, there's another 35 in the next circle and another 100 on the outside. And that's one person's social world.
I haven't run the numbers for myself, but the basic concept sounds plausible. I'm not quite as convinced by another argument the article raises — that people with more friends in school make more money later in life — but the rationale (social skills help in the workplace) isn't totally unreasonable either.