Powdered or confectioners' sugar is granulated sugar that has been crushed into a fine powder. To prevent clumping, a small amount (about 3 percent) of cornstarch is added. Powdered sugar must generally be sifted before using. Because it dissolves so readily, it's often used to make icings and candy. It's also used decoratively as a fine dusting on desserts. One and three-quarters (packed) cups powdered sugar equals 1 cup granulated sugar. Powdered sugar is called icing sugar in Britain and sucre glace in France.