Friendship takes time to develop. The more time two people spend together, the more likely they are to be friends. On the other hand, there are people we see regularly but don’t consider friends. So just how many hours of togetherness does it take for an acquaintance to become a friend? Or for a friend rise to the level of best friend? And does it matter what you spend all that time doing? For the first time, there are answers: 50 hours, more than 200 hours, and yes, it does matter.
These answers come from a newly published report in the Journal of Social and Personal Relationships by Jeffrey Hall, a professor of communications studies at the University of Kansas. Hall was motivated in part by the work of evolutionary psychologist Robin Dunbar of the University of Oxford who theorizes that there are layers of friendship—e.g., acquaintances, casual friends, friends and good friends—and that there are cognitive limits to the number of people that we can accommodate in any one layer. Those limits have a mathematical elegance. We usually are closest to no more than five people, call about 15 people good friends and 50 friends. Famously, Dunbar found that 150 is a rough limit on the number of meaningful relationships our brains seem able to manage.
To that idea Hall added his own, the Communicate Bond Belong theory, which asserts we all feel an evolutionary need to belong and that both the amount of time and the type of activity shared with a partner are strategic investments to help us meet that need. Previous research by Dunbar, Hall, and many others has established that time spent together matters in establishing connection, but no one had actually counted the hours.
In the second study, Hall recruited 112 brand new University of Kansas freshmen and asked them to name two new acquaintances. Then he followed up twice over the first nine weeks of the school year to measure time spent with those new acquaintances and see how the relationships had changed.
The results of both studies confirmed that time spent together was associated with closer friendships. “I was looking for cut off points,” Hall says, “where there was a 50 percent greater likelihood you switch from acquaintance to casual and from casual to friend, then again from friend to a close friend.” He found that it took about 50 hours of interaction to move from acquaintance to casual friend, about 90 hours to move from casual friend to friend, and more than 200 hours to qualify as a best friend. Those who never got beyond being acquaintances usually had spent no more than 30 hours together—the equivalent perhaps of being in the same class a few hours a week, but not seeing each other outside of the classroom. On the other hand, time together didn’t automatically make two people friends. Some adults reported spending hundreds of hours with colleagues but still called those people acquaintances. Basically, they just didn’t like them very much. Or they had no relationship outside of work.
Lydia Denworth is the author of two books of popular science, most recently I Can Hear You Whisper. She’s working on a book about the biology of friendship and is also a regular contributor to Scientific American, and blogger for Psychology Today.
This post originally appeared on Psychology Today. Read the original article here.