This is a pretty neat website - you select the number of participants and the county.
For example, if you have a gathering of 15 people in Las Vegas you have an estimated 25% chance of sharing a meal with someone Covid positive. If you were in New York City it would be 11%. In some counties in South Dakota, you're pretty much guaranteed to be with a disease vector according to the estimates.
Of course a lot of people believe that their relatives and friends could never be infectious. That will lead to some Christmas funerals.
COVID-19 Event Risk Assessment Planning Tool