Undecided

Start with a high MTU value (say 1500)

ping www.google.com -n 1 -f -l 1500

If the response includes

Packet needs to be fragmented but DF set

then lower the -l value by 10 and re-test.  Once you get a reply from your target address, increment the -l value by 1 until you cannot increment -l without receiving the above framentation message as a ping result.

This is your maximum MTU