For over a month now, Americans have been urged to practice social distancing and thus slow the spread of the novel coronavirus. Specifically, that has meant learning to try to stay six feet away from other human beings whenever possible.

What you may not know, and what even some of the top experts in the country still have questions about, is why six feet is the standard.

The premise of social distancing, also known as physical distancing, is that increasing the space between people decreases the likelihood one person will transmit COVID-19 to another. On a grand scale, this has produced federal guidance against gatherings of more than 10 people. Likewise, most states have enacted some form of “shutdown” or “lockdown”—mostly by way of shelter-in-place or stay-at-home orders.

On an interpersonal level, social distancing remains pretty simple. As the Centers for Disease Control and Prevention (CDC) explains: “COVID-19 spreads mainly among people who are in close contact (within about 6 feet) for a prolonged period. Spread happens when an infected person coughs, sneezes, or talks, and droplets from their mouth or nose are launched into the air and land in the mouths or noses of people nearby. The droplets can also be inhaled into the lungs.”

While six feet may be the standard, when in doubt, more distance is better, according to Dr. Timothy Brewer, professor of epidemiology at the UCLA Fielding School of Public Health who has advised the World Health Organization and the CDC.

“Being farther away reduces the chance of coming in contact with infectious droplets,” he told The Daily Beast.

The size of the droplets dictates how far they fly from a mouth or a nose. Six feet is, by most researchers’ estimates, outside or at least on the far edge of the splash zone.

“Individuals infected with respiratory viruses such as COVID-19 tend to produce droplets larger than 5 microns when they cough, sneeze or talk. Because of their size and weight, these droplets usually fall to surfaces within about a 3 to 6 foot distance,” said Brewer. “Any susceptible person within 3 to 6 feet of an infected person could have these droplets land on them and possibly become infected.”

Part of why the novel coronavirus is causing such havoc appears to be because it’s more durable than some predecessors. The officially-suggested distance between people is meant to make up for the amount of time the virus remains ambient and infectious, which is comparatively long.

“Viruses can’t survive without a host, but this virus is more contagious than others because it can survive outside you much longer—on metal surfaces for hours, even a few days on certain things,” said Dr. Anna Yeung-Cheung, a professor at Manhattanville College who studies virology. “So if we’re waiting for a bus and you sneeze, the closer you are, the higher chance your droplets have of landing on me—hand, shirt, face—and I breathe them in or touch my eyes.”

Complicating matters is that a growing array of experts and studies have pointed to the potential for “aerosol” transmission, where smaller droplets—tinier than the 5 microns Dr. Brewer mentioned—are in play. That could mean a wider infection radius.

“I’m skeptical that this is all contact or droplet transmission and not inhalation of small particles into the lower respiratory system,” Dr. Lisa Brosseau, an expert on respiratory protection and infectious diseases, recently told The Daily Beast.

Dr. Harvey Fineberg, head of the Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats at the National Academies of Sciences, Engineering and Medicine, echoed that perspective in a recent interview with The New York Times. “The virus is so small, it can hitch a ride even on tiny, tiny particles,” Fineberg said. “But how important is each size and how well they can transmit disease is not fully understood.”

Still, the Center for Disease Control has, at least so far, held fast to the six foot rule of social distancing throughout the coronavirus crisis. (The World Health Organization, or WHO, recommendation is actually less, at three feet.) And there are steps you can take in addition to keeping your distance. According to the WHO, “Make sure you, and the people around you, follow good respiratory hygiene. This means covering your mouth and nose with your bent elbow or tissue when you cough or sneeze.”

And, in keeping with recently-updated CDC guidelines, people should wear a face-covering or mask when in public, even if the evidence of their efficacy is less than spectacular.

Though personal space and the spread of the virus are inversely correlated, you do not necessarily need to maintain six feet of distance between yourself and other members of your household like roommates and children, local health officials have said. You should, however, continue to avoid visitors in your home—and avoid common areas like lounges if you live in an apartment building.

The effects of coronavirus have been undeniably horrific. But it’s possible to use your imagination in lighter fashion when practicing social distancing. To measure six feet quickly, the American Red Cross recommends picturing “two large dogs standing nose to tail” in between you and the next person.

And given evolving concerns surrounding aerosol transmission, maintaining more than six feet of distance from others whenever possible is the safest move.

Editor's note: This story has been updated to correct Dr. Anna Yeung-Cheung’s title at Manhattanville College.