Depending on where your event is happening, there maybe some guide lines that you need to follow. Below is the Nevada statue (NRS 444.825) that shows the required number of porta potties.

The Americans with Disabilities Act (ADA) requires one handicap porta-potty for every 20 standard units, or at minimum one per event with potties

If your event is multiple days, use the longest day for the amount of hours and the largest audience for the audience size

For events with alcohol, plan to have 15 - 20% more porta potties

Have one handwash station per 4 restrooms

For events with food handlers, we do have heated handwash stations that reach up to 130 degrees Fahrenheit