The answer according to one academic is 151 when it comes to Facebook friends. It appears that is the stage at which your Facebook friend list becomes unmanageable. The reason is that our brains are simply not big enough for us to handle meaningful relationships with more than a handful of people. Apparently there is a general relationship between brain size and social group size in monkeys and apes. That relationship predicts a natural group size and for humans this size is 150. This number is among other things the average number of people we send Christmas cards to, the average size of parishes among community-focused sects such as the Amish and the Hutterites, and the typical size of companies in most armies. Within these friends your social world then contains circles of friendships from a core of more intimate friends declining in intimacy down to those on the outskirts. I currently have 94 Facebook friends so it appears I have extra capacity for a few extra.