I gave a keynote at one of the major academic conferences in my field. Not sure the exact number but at least a couple thousand people.
At a different conference I gave an invited talk in a symposium. Due to logistics the symposium was the last session on the last day of the conference. The only people in the audience were the other 5 speakers. We gave our talks to each other and hit the bar.
Probably 30 people at most. I held computer classes at a job I once had, and that was about the largest attendance we had. I usually got good feedback by the participants, but actually I’m not a good speaker. I always have too much pauses and eh’s mixed in, and also sometimes struggle to find the right word. I don’t have these problems when I’m writing though, the words just flow out of my fingers to the keyboard or the paper, but I’m bit of an introvert, so that explains it.
I would have hit the bar first and then give the talks. 
Believe me, it was discussed. But it was a session where we were all working on the same related topic and we were interested in what each other were doing, so we did the talks. Much more informally than typical of course.
It was actually great.
I gave the eulogy for my brother for about 500 people (my brother was very well liked). I was also the emcee for my mom’s 80th birthday party, which was about 400 or so (my brother, while well liked, didn’t want to take the mike even though, as the eldest, it should have been his responsibility). I spoke at a professional conference for about 450-500, presenting to a sometimes hostile crowd (which, coincidentally, included a guy who had been trying to seduce my wife - fun times). And every year I get onstage for a crowd that numbers anywhere from about 100 to maybe 1000, but most of whom aren’t paying attention.
I don’t fear public speaking, probably because I got a lot of practice in junior high speech class, where I would regularly be underprepared when it was my turn to speak, so I had a lot of extemporaneous deliveries. Some were terrible, probably painful for my audience/fellow classmates, but I learned a lot from it and I got better at both preparing AND speaking off the cuff.
I was an activist in the peace and environmental movement while in university and in my later twenties. Spoke at several rallies of hundreds of people during the first Gulf War. I organized a quite large event when some representatives of a native group from Borneo came through on an awareness tour. Someone more suitable MC’d, but I came up on stage at the end of it to say a few words. That was a couple thousand people I think. Long time ago.
The last, and most significant time I spoke in front of a group was for the memorial of my very close friend that died suddenly a couple years ago. That was in front of maybe a hundred people. It was my chance to share my experience and admiration of a very special person with the group. Having all that previous public speaking experience allowed me to deliver a fitting eulogy focusing on the joy he took in life. Proud of that moment.
I was at a workshop in Santa Barbara once where the event was being bussed on a wine tasting tour, including dinner. There was a lot of wine at dinner. Then we all came back for a panel.
Not a good idea.
Growing up as a Mormon, we regularly gave talks in church to a hundred or more people. As an adult I’ve had to give various presentations to difference sized audience, the largest was several hundred.
When I was younger I was a semi professional magician and the largest audience was 600 or so. It was actually less intimidating than smaller groups of less a couple of hundred because the larger groups had the lights dimmed.
Probably not more than a couple dozen at work. I was in some school plays where I would guess there were a few hundred people in the audience but I don’t know if that really counts.
I actually just had the most nerve-wracking public speaking in my life last week. There were only seven people in the room but one of them was the company CEO and my boss was like “oh by the way, you’re presenting part of this” on our way to the meeting.