Confectioners sugar is a processed version of table sugar that is ground very fine. Cornstarch is added to confectioners sugar to keep the fine powder from clumping and sticking. In a recipe, confectioners sugar may be substituted for table sugar if that is all that you have available. Using powdered sugar instead of standard granulated sugar can alter the final baked good due to the addition of cornstarch in the powdered sugar.
Read your recipe to determine how much table sugar is necessary.
Calculate how much powdered sugar to use. For every cup of table sugar, use 1 1/3 cup of packed powdered sugar.
Measure the amount of confectioners sugar needed per your calculation. Pack the powdered sugar into the measuring cup by pressing down on the surface of the sugar. Packing the sugar will provide the most accurate measurement for substitution.
Add the powdered sugar substitution to your recipe in place of table sugar.
Bake the mixture as directed by the recipe.