A recipe calls for caster sugar, and the nearest bag says confectioners’ sugar. Both sound finer than regular granulated sugar, but they aren’t the same ingredient. Caster is superfine granulated sugar. Powdered sugar is a separate product.
Before choosing a substitute, check which kind the recipe names and how it’s used. Here are the questions that usually settle the shopping decision.
What does “caster” mean on a recipe?
Caster, also spelled castor, is a name used for superfine sugar. Its crystals are smaller than ordinary granulated sugar crystals. King Arthur Baking’s sugar guide identifies it as a quick-dissolving option for uses such as meringues and egg foams.
You may also see a product sold as baker’s sugar. Read the product description instead of relying on “fine” somewhere on the front of the package. King Arthur’s Baker’s Special Sugar, for example, is explicitly described as superfine.
Is confectioners’ sugar just another name for it?
No. Confectioners’ sugar is powdered sugar. Domino describes its powdered sugar as granulated sugar ground into a soft powder, intended for uses including frosting and glaze. That product category isn’t a shopping synonym for caster sugar.
If your recipe asks you to dust a finished dessert with powdered sugar, buy that ingredient. If it calls for caster sugar in the batter, don’t take the dusting ingredient as a substitute simply because it looks finer.
Can regular granulated sugar replace caster sugar?
King Arthur’s guide allows granulated sugar in place of superfine by weight and suggests processing it finer when possible. That’s guidance for a substitution, not a promise that every recipe will turn out exactly the same.
Start with the recipe developer’s own notes. If a particular recipe explains when or how to make the swap, keep that instruction with the recipe. Don’t combine a change of sugar with several other ingredient changes and expect to know which one affected the result.
For a bake where the outcome matters, getting the specified sugar is the more direct route. A substitution can wait for a separate batch that you have time to assess.
Should I measure the same number of cups?
Use the recipe’s gram amount when applying weight-based substitution guidance. “By weight” and “cup for cup” are different instructions. If the recipe gives only cups and no substitution note, ask its developer or choose a version written for the sugar you have.
Write the actual sugar and amount in your notes if you do change it. “Used superfine, 150 g” is more useful next time than “used the other sugar.” Keep any observations about the finished bake with that note. The brown sugar guide covers another label distinction that often comes up at the baking shelf.
Sources and photograph
King Arthur Baking and Domino product and baking references checked October 22, 2026. This is an ingredient-label guide; Replicate Kitchen isn’t claiming a side-by-side substitution test. The stock photograph illustrates whipped egg whites, not the result of a sugar comparison.
