Depends on the aircraft and time period. They generally weren't based on a ratio. If you specify a particular aircraft, I may be able to be more specific but here are some common ones:
FW190 Upper lower wing 910mm, fuselage 800/810mm
Bf 109G Upper wing 1000mm, lower wing 950, fuselage 950
Variations also existed within these. Source: Luftwaffe Colours 1935-1945 by Ullmann.
Thank you Crimea, those are the figures that I am looking for. I'm trying to compile a list of all balkenkreuz sizes by aircraft. I picked up "Luftwaffe Camouflage of WW2" by Philpott but I don't see this type of information in it.
Does the book that you refered to contain a good listing of balkenkreuz sizes?