Powdered sugar right out of the box or the plastic bag weighs 4 1/2 ounces per cup, so a 1 - pound box (or 16 ounces) contains about 3 1/2 cups.
Convert how many pounds (lb) of powdered sugar are in one 1 US cup (cup us). This online cooking powdered sugar conversion tool is for culinary arts schools.
1 pound brown sugar = 2 1/4 to 2 1/3 cups. 1 pound confectioners sugar = 3 3/4 cups unsifted. For information on other different types of sugars.