A 1-pound box of powdered sugar contains approximately 3 ¾ cups of unsifted powdered sugar. A 2-pound box contains approximately 7 ½ cups of powdered sugar.
Manufacturers create powdered sugar, which is also commonly called confectioner's sugar, by milling granulated sugar with a small amount of cornstarch. Powdered sugar has a fine consistency that allows it to dissolve quickly in any liquid. Store powdered sugar in a cool, dry spot.
Cooks who are out of powdered sugar can swap ½ cup and 1 tablespoon of granulated sugar for 1 cup of powdered sugar, although the substitution does affect the texture of the finished product.