Looking up again on Wikipedia, A=400 is an international standard - ISO 16.

Of course that doesn't mean everyone follows that. Wikepedia lists New York Philharmonic and Boston Symphony orchestras using A=442, Most modern German and Austrian orchestras at A=443, mentions the baroque tunings McGrath gave, etc.


Lowest pitch I found mentioned was A=380 (1720 English pitch pipes) and the highest I've found is A=480 (some organs played by JS Bach). Apparently that's around 4 semitones difference.