According to a recent study, four.

The paper, titled “Do online social media cut through the constraints that limit the size of offline social networks?” was published by the Royal Society of Open Science and takes a look at whether social media networks have expanded our real-life social networks.

Robin Dunbar, a professor of evolutionary psychology at the University of Oxford, conducted two surveys: one that sampled 2,000 social-media using adults across the U.K., and another that included 1,375 professional adults who work nine-to-five weekday jobs.

While the average person had 150 Facebook friends, only 4.1 of those could considered friends you can count on for support and assistance in a time of crisis.

Expanding out to a “sympathy group” – those you might consider close friends – left an average of 13.6 people.

Dunbar has also published a paper that stated humans can only handle approximately 150 meaningful relationships at once.

Dunbar also concludes that online social networking sites like Facebook don’t seem to help individuals expand their true social networks larger than they would if they stayed strictly offline.