Sugar has many forms because it does much more than simply sweeten food. The basic difference between granulated sugar and powdered sugar is that powdered sugar is ground more finely than granulated. Powdered sugar usually contains about 3 percent cornstarch as an anti-caking agent. Both the texture and composition influence how sugar affects the recipe you use it in.
Basic Weight/Mass Equivalent
Granulated sugar weighs more than the equivalent mass of powdered sugar. Because of this, use 1 3/4 cup powdered sugar for every 1 cup of granulated sugar you need. A straight substitution will not always yield the same result because of how sugar functions in recipes.
Function of Sugar in Recipes
Avoid powdered sugar in any recipe that needs air incorporated into the batter, such as a cake batter that starts with creaming butter and sugar together. Doughs may need granulated sugar because of its tenderizing and water-absorbing qualities and powdered sugar cannot provide these. Because of the light cornstarch taste, powdered sugar is also not a good idea in drinks such as coffee or punch. The cornstarch may also cause a cooked sweet sauces to thicken more quickly and to a higher degree than expected. Powdered sugar in a cookie dough will give you chewier cookies. You can also substitute powdered sugar for granulated for decorative purposes, such as dusting finished baked goods before serving.