Using 3-D simulation data from the Kyoto Institute of Technology, The New York Times shows how droplets from a sneeze or a cough can spread in a space. In a nutshell, six feet is the recommendation while in public areas, but the farther you away you can stay away the better. Go to the end, and there’s also an augmented reality segment that puts a six-foot range around you.
I may never set foot in a crowded place again.
See also: how different cough coverings can change the spread of droplets.