If you're wondering how many people you can call your best friends, it depends on who you ask: Harry Potter had two, six on Friends, and Myspace only had eight slots for BFFs. But according to new research from Oxford University, it doesn't matter how many people you think are your best friends, because there's only enough room in your brain for five.
In the 90s, British anthropologist Robin Dunbar theorized that humans had the brain capacity for a max of 150 meaningful relationships, separated into tiers containing five best friends, ten other friends, 35 acquaintances, and 100 contacts that you basically just wish a happy birthday to on Facebook.
More recently, Dunbar took this same logic and studied cellphone records made by 35 million people in 2007—before the rise of smartphones and social media—to judge the closeness of relationships by the number of shared phone calls. Dunbar found that, on average, people had 4.1 best friends, 11 close friends, 29.8 acquaintances, and 128.9 other contacts.
The study showed that both introverts and extroverts have the same capacity for Dunbar's proposed social tiers. MIT Technology Review pointed out that analyses of other social networks, like Facebook and Instagram, could yield even more interesting data—especially because your thousands of "friends" on Facebook are probably not your friends at all.