The magic number is 150
Created by British anthropologist Robin Dunbar, this number is a theoretical, finite value of 150 which indicates the maximum number of individuals there can be in a group of people with tangible social relations. Tangible social relations mean that each individual knows one another (light conversations, or at least know their names) and also that each person knows the relationships among everyone else in the group. For example, if there was a small school grade of 150 kids, they would all know each other’s names, including a basic description of each other, and any sibling relations there may be between the classmates.
In the case that a group consists of more than 150 people, a system of laws, regulations, restrictions, and rules is necessary in order for the group to function properly in any matter. This would stem into organized governments and 'micro-managing' or having groups of people in charge of other groups of people. This holds especially true when the matter involves cooperating and/or communicating with another social group.
Dunbar later theorized that this number is mostly valid for communities with strong motives to stay closely related, especially for purposes of survival. In addition, if the number of the members within the group exceed 150, conflicts among the individuals are more likely to occur than if they were at or below 150; there are bound to be multiple opinions on any issue that needs to be discussed within the group, and the more opinions (and different types) there are, the harder it becomes to satisfy everyone’s needs, and therefore, the harder it becomes to sustain the group for any period of time.
So do you think 150 is a lot? Try to count all the family members and friends that you would actually cry for if they were to pass away. Some people may be very social and have more than 150 they care for while others may have a lot less. Spread between personal and work life, you might be surprised with the number of people you actually know and care for.
Now you might be thinking this is all a bunch of mumbo-jumbo but there have been comprehensive studies. Robin Dunbar was very wise comparing human groups to monkeys.