The best replacement for caster sugar is powdered sugar.

The best alternatives to caster sugar are rated as following:
★★★★★  powdered sugar
★★★★★  icing sugar
★★  golden caster sugar
★★  granulated sugar
★★  regular sugar
★★  granulated
★★  white sugar
★★  confectioners sugar
★★  cane sugar
★★  normal sugar
★★  confectioners
★★  bakers sugar
★  castor sugar
★  superfine sugar
★  caster sugar
★  fine sugar
  light brown sugar
  muscovado
  demerara

Your alternative for caster sugar is not listed? Suggest!
Speaking about caster sugar, one probably shouldn't forget about icing sugar.

Other search terms related to caster sugar and their ratings are:
★★★★★ icing sugar
You have in mind a companion for caster sugar and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of caster sugar in all years. Click on graph for more.
caster sugar
powdered sugar
icing sugar