There really isn't an exact formula for such things. It all depends on what chemical you are using to alter the octane............beyond that, octane is poopulary determined via reasearch and test motor figures, which you really can't come up with on your own at home.
Octane boosters are a generally a bad deal. If you cannot get race fuel or alcohol, you may need to consider configuring your engine for what you can get ahold of. :thumbsup: