...lai gan, internets met ārā šādu info:
Multiply the amount of granulated sugar called for in the recipe by 1.75. For example, if the recipe calls for 1/2 cup of granulated sugar, you will need 7/8 cup of confectioner's sugar.
It's about 1 3/4 cup of powdered sugar for every 1 cup of granulated sugar.
Ja tev ir svari, vienkārši nosver glāzi cukura un glāzi pūdercukura. Nu un, attiecīgi, izrēķini proporciju.