There is no such thing as perfect safety. If you live in an apartment, even if you stayed home 100% of the time, viral particles could potentially make it through a faulty ventilation system. (This may have been the cause of numerous SARS infections in 2003 at a Hong Kong apartment building called Amoy Gardens Block E…see p. 137 of SARS in China: Prelude to Pandemic?).

So how do we know what is reasonably safe to do and what isn’t? Enter the microCOVID Project, a research-based calculator that can estimate the risk of contracting COVID from virtually any activity.

The calculator uses your location (and its COVID prevalence) along with other assumptions (who is near you during an activity, what mask they’re wearing, etc.) to calculate how likely you are to get COVID in a given situation. For example, going to the grocery store for 60 minutes in my area is 200 microCOVIDs. This means that if I went to the grocery for 60 minutes once a week every week for a year, I’d have a 1% cumulative chance of getting COVID from that activity.

Play around with the assumptions. For example, the grocery scenario assumes I’m wearing a cotton mask. I don’t do that. Instead, I wear a KN95 mask from the FDA approved list, which cuts the risk in half, to 100 microCOVIDs.

Is this calculator perfect? I’m sure it’s not. But it provides a useful way to estimate risk and decide if an activity is worth it to you or not. In a time when we are forced to think about risk more than usual, it is a valuable tool!