The largest opera house in Europe is the Bastille Opera house in Paris with a capacity of over 2700 seats.
2,268
500
The largest Opera House in the world according to the number of seats is the Metropolitan Opera House in New York City. It has 3,800 seats and more than 300 spaces for standing room. It's followed by Chicago's Civic Opera Theatre which is home to the Chicago Lyric Opera. The Civic Opera Theatre has 3,560. Cincinnati's Music Hall, home of the Cincinnati Opera ranks third with 3,516 seats. Theses housed dwarf the European houses of which the largest only hold around 3,000 people. Milan's La Scala for example has only 2,800 seats and London's Royal Opera House at Covent Garden has 2,268 seats. The Arena in Verona can seat up to 20,000. While it could be argued that it is not an opera house as it does not have a roof and it was built for gladiators, it has been staging opera for 100 years - much longer than the Met!
A full house seats about 3,800 people.
The opera house in Beijng can seat in total 5452 in thee halls (Opera Hall 2416, Music Hall 2017, Theater Hall 1040)
The five venues making up the main performance facilities: The Concert Hall - 2,679 seats. The Opera Theatre - 1,507 seats. The Drama Theatre - 544 seats. The Playhouse - 398 seats. The Studio - capacity of 400 people.
At 1900 seats, the Gershwin is the largest of the Broadway theaters
The present Metropolitan Opera House, with approximately 3,800 seats located at Lincoln Center at Lincoln Square in the Upper West Side.
Once you go outside the top 3 it becomes subjective [seating / standing etc] taking purely opera houses that are the homes of opera companies and not just where opera is performed at times [example Beijing Grand Theater seats 6,500] the top 3 are - Metropolitan Opera House in New York City Chicago's Civic Opera Theatre Cincinnati's Music Hall
The New York Met Opera house Web site states that there are approximately 3,800 seats in the auditorium. You added Sydney to your categories, and the Sydney Opera Theatre, a proscenium theatre seats 1,507, and there are other theatres in that complex.
The five venues making up the main performance facilities: The Concert Hall - 2,679 seats. The Opera Theatre - 1,8900 seats. The Drama Theatre - 876seats. The Playhouse - 78 seats. The Studio - capacity of 467people.