Harvard’s full Admissions Committee is comprised of over 40 members, half of whom are professors:
http://news.harvard.edu/gazette/story/2015/04/harvard-college-admits-1990/
And it’s one-person, one-vote! Every accepted student must receive a nod from at least 51% of the people in the room. If every member of the full committee happens to be present that day, that means each student needs at least 20+ people in the room saying “YES” for them to be accepted.
It’s important to remember though that not every student is brought before the full committee. Regional Admissions Directors and the regional admissions committees read files and only bring the strongest applicants to the full committee.
My guess is that between the SCEA and RD cycle maybe 3,000 to 3,500 students who have it all – top grades and test scores, stellar teacher recommendations, thought provoking essays, good interview reports and remarkable extracurricular activities – are brought before the whole committee each year. Of those 3500 students, about 2100 of them are made an offer of admission. The 1400 or so applicants who are not chosen by the full committee probably go to the waitlist.
The vast majority of applicants – probably 85% to 90% of students who apply to Harvard never make it to the full committee. That’s because their Regional Admissions Director had other top candidates to choose from.
Here’s a good article too read: http://www.bostonmagazine.com/2006/05/keys-to-the-kingdom/
Best of luck to you in the Admissions process!