What quantity of baking powder satisfies a mass of size x?
About 5g baking powder per 150g flour, or about 1tsp of baking powder per US Cup of flour (Source: Michael Ruhlman's Ratio app.) That will work for most chemically leavened batters, quick breads, pancakes, etc. This is a guideline, not a rule. 
Sometimes more leavening is desirable— you might want a slightly puffier quick bread and you're using a dough with enough protein to handle it. Maybe you want less because you've got a batter that doesn't stay together on something you're frying.

Unless you're planning on doing some workshopping, I recommend using an existing proven recipe to get a good ratio of ingredients. After a while, you'll get a better idea of how much leeway you've got with each variable in the technique.