Ha! A timely question. On the 4th, I am going to anchor out to watch the fireworks...my daughter wanted to invite some friends. "Sure", I said, "how many"? "8-10"
Hmm...8+4=12 minimum. Seems a mite overcrowded to me, even though we won't be sailing - especially with 8 who had never been on a boat before. So I was a Grumpy Old Man and limited it to 4 extras (i.e. 8 total).
A lot depends on what you are doing, and the weather conditions. If you are just motoring around, you can carry a higher number. In light winds, fewer. In heavy winds, even less. Racing, you to balance space with hands to move fast! (And before you ask I am still almost last :-)
I think the ideal for racing is 5 (nav/spotter/skippper, helm, 2 jib sheets, 1 mainsheet.) We often carry 6 in the cockpit, anything above that is railmeat. 6 does get a bit crowded when things are getting a bit windy and we are all on the uphill side. Recreational sailing, 6-8 max.
I'd also be interested in what others say!
I think we could safely carry more, e.g. down below, but not a lot of fun for them.