For standing room, the general rule of thumb is allowing for 6 square feet per person.

Equation: The square footage of your space divided by 6.
Example: a 500 square foot space /6 = 83

If you plan to have guests be distanced, increase the number of feet divided to offer more space per person.

For seated events, determine how many seats you can fit into the entertainment space, while still giving the artist plenty of space to perform.