That's not a clear cut question. They usually give you a starting point and then it has to be adjusted to fit you.
As someone similarly said before, if I am too high, say over 9, it takes more to bring it down than if I want to lower it from a 7.
Activity level also makes a big difference on how much I need, and night time I need a little less to correct.
It really is a learning curve on exactly how much and we don't always get it right. Trial and error as said before! Keep track of how you respond and you will learn!