From The New York Times (April 14, 2020):

But as this simulation suggests, and scientists have argued, droplets can travel farther than six feet. And small droplets known as aerosols can remain suspended or travel through the air before they eventually settle on surfaces. This is how they could disperse over the next 20 minutes.

The Centers for Disease Control and Prevention encourages people to stay home. If you must venture out, you should stay at least six feet away from others. The World Health Organization recommends a minimum of three feet of separation.

Scientists are learning about the novel coronavirus in real time, and those who study similar respiratory illnesses say that until it is better understood, no guideline is likely to offer perfect safety. Instead, understanding the possible transmission routes for the virus can help us see why keeping our distance is so important.

View 3-D simulation