While sizes may vary, a 1-pound box of powdered sugar yields roughly 3 3/4 cups of sugar. A 2-pound bag of powdered sugar yields approximately 7 1/2 cups and a 4-pound bag yields 15 cups. Powdered sugar is also known as confectioner's sugar.
Boxes of granulated and brown sugar yield different amounts. A 1-pound box of granulated sugar yields 2 1/4 cups of sugar, while a 1-pound box of brown sugar yields 2 1/2 cups of sugar. This is in part due to the difference in density between the types of sugars. Powdered sugar is often used in recipes for frosting, fudge, glazes and candies.