Four cups will be roughly equivalent to one pound when measuring powdered sugar.
How many cups does one pound of powdered sugar contain?
Powdered sugar directly from the box or plastic bag weighs 4 1/2 ounces per cup; therefore, a 1-pound box (or 16 ounces) provides approximately 3 1/2 cups of powdered sugar. If a recipe asks for powdered sugar, 4 ounces of powdered sugar will equal 1 dry measuring cup.