The microCOVID Project is a service that uses the best available data to estimate the risk of different activities. It does not replace advice from a medical professional, but as a way to deciding how to balance risk, it can be useful. It computes “microcovids,” a one in a million chance of getting covid: every 10,000 microcovids means a 1% chance of getting covid at the event.

Microcovid.org’s point estimate the percentage chance of getting covid in a one hour lecture for someone (the rows) with a classroom of people with vaccination state matching that of Knox County and with different masks as columns. You can see the details of the scenario I set up here; you can change your vaccination and masks, the classroom’s conditions, etc. Note that the numbers are the odds of the focal person getting covid; it does not capture how severe the disease is (vaccination dramatically cuts the risk of death if you do get covid, for example):

unmasked cloth N95
Boosted & N95 1/NA (NA%) 1/Inf (0%) 1/Inf (0%)
Vax but no booster & cloth 1/167 (0.6%) 1/333 (0.3%) 1/1000 (0.1%)
Not vax, no mask 1/125 (0.8%) 1/250 (0.4%) 1/1000 (0.1%)

And the same probability of getting covid over six class sessions with these conditions;

unmasked cloth N95
Boosted & N95 1/NA (NA%) 1/333 (0.3%) 1/1000 (0.1%)
Vax but no booster & cloth 1/29 (3.5%) 1/56 (1.8%) 1/167 (0.6%)
Not vax, no mask 1/21 (4.7%) 1/42 (2.4%) 1/167 (0.6%)