How big was the largest orchestra?

Answer 1

The world's largest orchestra gathered in BC Place Stadium., in Vancouver, Canada. It was comprised of the entire Vancouver Symphony Orchestra, plus about 6400 band students, who came from about 160 across the province. They played an arrangement from Beethoven's 9th Symphony, for 9 minutes 44 seconds. The old record was set in Birmingham, England when 3500 musicians got together to play for secen minutes and 42 seconds. Ben B. Source: my sister was in the orchestra.

Answer 2

The Royal Albert Hall staging area is 104 m2 but the Bridgewater Hall in Manchester has a staging area of 227 m2.

From Barron's book 'Auditorium Acoustics and Architectural Design' I'd say the usual sizes of the stages was between 155-180 m2.

Orchestras tend to spread into whatever space you give them.