When I use powdered sugar, it's usually in a "per 2 lb bag" amount; seldom do I measure. (I make a lot of buttercream and have you every worked with powdered sugar? That stuff goes everywhere, it's just easier to dump the whole bag into the mixer!)
So, what happens when I come across a recipe that calls for cups of powdered sugar rather than a whole bag? Well, I know that 2 lbs of powdered sugar equals roughly 7 1/2 cups (or if I really don't feel like working with fractions, 8 cups), so I can go from there to determine if I need to double or triple a recipe to get to my usual "per bag" measurement. Luckily, buttercreams and glaze icings are pretty forgiving and you can add powdered sugar or liquid to reach the right consistency.
Here's the commonly accepted amounts when it comes to powdered sugar measurements:
- 3 3/4 cups = 1 lb
- 7 1/2 cups = 2 lbs
- 15 cups = 4 lbs
Note that these conversions are based on unsifted powdered sugar.
Oh, and did you know confectioners sugar and powdered sugar are the same thing? Powdered sugar is also the same thing as icing sugar and 10x sugar - it just depends on where you are as to what it's called.