Using Powdered Sugar (Icing Sugar) Instead of Caster Sugar
Ratio
1:1 by weight, only where sugar fully dissolves
Moderate — noticeable differences, use with care
Recipe Adjustment Notes
Contains about 3% cornstarch — fine in icings and some doughs, wrong for creaming or meringue.
The Science Behind This Swap
Particles are too fine to cut air pockets into butter during creaming, and the added starch changes texture in high-sugar recipes.
Measurement Variance Note
For 1 cup references, this ingredient can vary by about 8% across brands and measuring methods (175g-205g per cup). For the most reliable substitution result, measure by weight and test a half batch first.
How Powdered Sugar (Icing Sugar) Compares for Caster Sugar
Quality rating: moderate. Contains about 3% cornstarch — fine in icings and some doughs, wrong for creaming or meringue.