Development of the Orchestra

Nowadays, the number of full-time players in an orchestra is almost standardised in most places around the world. And we audience are only able to see the conductors back. 
Look at how the orchestra evolved!

Moreover, orchestral size has always been subject to variation. The gradual increase was initially connected to the transfer of the orchestra from royal courts to the public domain.
In 1782, the permanent staff of the Mannheim Orchestra included 33 stings players and 21 winds players. At the time of Berlioz, his symphonie fantastique demanded more than 50 strings players. At the time of Mahler, the number of orchestra players went up to 120 for his 8th symphony.

Settings of a Baroque orchestra

A modern full-scale symphony orchestra consists of approximately one hundred permanent musicians, most often distributed as follows: 16–18 1st violins, 16 2nd violins, 12 violas, 12 cellos, 8 double basses, 4 flutes (one with piccolo as a specialty), 4 oboes (one with English horn as a specialty), 4 clarinets (one with bass clarinet as a specialty, another specializing in high clarinets), 4 bassoons (one with double bassoon as a specialty). In theory, all woodwind players are expected to be able to play all auxiliary instruments in addition to their main instrument. Furthermore 5–8 horns, 4 trumpets, 4 trombones (one with bass trombone as a specialty), 1 tuba, 1 kettledrum player, 3–4 percussionists (of whom at least one must also play kettledrum), 1–2 harps and a keyboard player (piano, celesta, harpsichord, etc.).



And check out what Berlioz says about the orchestra and instrumentations!
http://www.hberlioz.com/Scores/BerliozTreatise.html