My father just got back from Singapore where he gave a speech to 4000 people. Even for someone who gives lectures and workshops all the time, that was a large crowd.
I doubt I’ve ever spoken to a group larger than 200 people.
What about the rest of you?
Maybe 30 people.
But there seems to be some upper and lower limit.
Below X its just conversation.
Between X and Y it’s “Public Speaking” and is scary.
Above Y is no different no matter how many you add.
I gave my Academic Decathlon speech my senior year of high school (during the Speaker Showcase) in front of about 600 or so individuals. (Won a first place medal for that speech, too.)
As part of an Honor’s contract two years ago, I had to deliver a presentation on Hate Crimes to the entire Honor’s Department and my college, which was roughly around 3200 students and faculty.
I moved past scared silly to operating on autopilot in the bginning, but the subject matter was something that always gets my adrenalin pumping so by the time I finished, it had been a very compelling presentation, or so I was told.
I’ve acted on stage in a tiny theatre - the most at once I have acted before is about 150 people.
I speak weekly in front of groups of about twelve. I am rarely able to eat before, but once I get going I am fine unless I am unprepared. I speak two or three times a year in front of around fifty. Twice I’ve spoken in front of about 350. I find the fifty and the 350 to both be tremendously terrifying. It starts with an undeniable uneasiness, then my knees knock, my breath balks, and I quiver quite uncontrollably. :o (Whew! I sure am glad THAT is over!)
Abby
Why didn’t my sig show up?
Oh, duh! I was supposed to check the box!
As a movie theater manager, our biggest house held 700 people, so whenever we had some news (“This is why your movie isn’t running”, “This is how long before the movie resumes”, “This is why you need to get a refund”, etc.), I was usually the lucky one–not exactly a speech per se, but also not something you want someone not comfortable speaking in front of large crowds doing.
I’ve done a couple off-the-cuff auctions occasionally; just some random stuff people bought as fundraiser efforts. Biggest crowd I spoke in front of was about 800 people at the final party of a conference.
I’m a ham. I loved it. 
50 or 60 people. I was asked to be one of the speakers for my paralegal program’s job workshop. (I guess their first thousand choices were too busy)
I only pissed my pants once. (kidding)
Seriously, they haven’t asked me back, so I must not have done too well. Then again, they still use me as a reference for people deciding whether to enter the program or not, so I can’t have alienated too many people.
It’s funny, I could never imagine speaking in front of hundreds of people, but there was a time that speaking in front of TWENTY would terrify me. I won’t say I enjoy public speaking, but at least I’m not as pathologically shy as I used to be.
About 120 people. I was supposed to speak in front of about 230 people at a conference recently, but since my presentation was the last one on the last day on an afternoon, less than 25 people were there. :rolleyes:
I used to give lots of presentations in front of crowds, the largest audience I ever addressed was about 1500. It didn’t feel much different than my typical speeches to smaller audiences like 200 people.
I did a stand-up comedy set before an audience of over 1000 a while back. I was at a club where a band was supposed to play but didn’t show up. The headline band wasn’t there yet, and the manager, who is a friend of mine, needed someone to kill time for twenty minutes or so. He asked me to play, but I didn’t have any gear, so I just got up onstage and told jokes. Went over fairly well.
Welcome to the SDMB, AbbySthrnAccent!!! Let me present you with your SDMB Membership Kit. It contains all that you will need to have here.
It has one (1) Laminate I.D. card. You may display this either in your wallet, OR using the handy clothing clip, attaching it to the left breast pocket of your uniform shirt or jacket. It also has two ( 2) Snickers bars, because one does one’s best work on a full stomach. One (1) MicroChip. This contains the sum total of all human knowledge. Use it wisely. Try not to get picante sauce on it, it’s rather sensitive to acids. :D. Two (2) pre-paid phone cards. These are to be used to contact your own personal SDMB Advisor, in case you are sloppy enough to get some picante sauce on aforementioned MicroChip. Five (5) road flares, so that when you are sitting by the side of the road, eating your Snickers bars and waiting for the tow truck to come because you blew out the alternator using your laptop and wireless modem to be on the SDMB when you should have been paying more attention to the traffic flow, you will be safe because you used all five (5) road flares in a diagonal pattern.
Enjoy your tenure here with us. It is a delightful and thought-provoking community. Please turn off the lights on your way out. 
Oh, and to answer the O.P.? I once had to perform in front of 3.2 billion people on live television. 
I win. 81,000 of them were in front of me, the rest were watching me on worldwide t.v. Thank god I didn’t fall down or something.
Cartooniverse
About 1200 I think, there were more people than bought tickets so it’s hard to say.
It was a final of the Icelandic national debating championships. We lost 
— G. Raven
Thank you for the welcome Cartooniverse. The message board and the membership kit are delightful! I am digging through contents and thinking, I sure hope there are some of those bright orange water wings in here.
However, I am waiting for the tow truck due to flooding. (I am not ready to admit SDMB addiction yet! )
Abby
My largest group was a little 4 or 5 minute speech convincing people to try out for my school’s Advanced Academics program. There were probably about 300 people there, on a generous estimate. Was I nervous? Yes. Did I pull it off and make the crowd laugh? HELL YES!! :D.
I speak in front of crowds of anywhere from 10-100 people a few times a week. The first time I did it, I was scared out of my mind. Now I barely even break a sweat.
To be honest, the bigger the crowd, the less self-conscious I feel. 15 is a group of individuals staring at you. 100 is just a faceless crowd.
–sublight.
Back when I worked for MassPIRG in college, I spoke to a number of lecture sections… maybe about 150 people or so. The campus organizer, Bill, was so cool, he knew I was terrified so he’d stand in the back of the room so I’d feel like I had some moral support. Once I did it a couple times, it got easier, but I was terrified the first few times!
…approximately 7,000 give or take one or two. 
Up til then I regularly addressed audiences of 1000 or so. The few additional folks didn’t phase me.