(Now we're not talking Facebook friends here, but meaningful friendships, and these can be broken down into groups:-
As humans we can cope with anything from 5 to 13 very close friends, the norm is 5. (The ones you can't afford to fall out with because they know too many secrets about you.)
An extra ten friends on top of that make up people you care about and mix with most.
Another 35 people create an extended circle of friends, friends from school, groups, work or clubs. And then a final 100 – acquaintances, kind of friends of friends.