Chaptalization calculator finds how much sugar to add to your must to hit the desired Brix. Chaptalization is the process of adding sugar to must early in wine making process to boost the Brix and thus the total alcohol in the finished wine. The purpose of adding sugar is to boost the Brix in a poor growing year and help the final product turn out better.
Do not go overboard with adding sugar! An overly alcoholic wine is just as bad as an over oaked wine, or any other defect.