US recipes, UK kitchens
How many grams are in a cup of icing sugar?
At Cupstograms, we use 113g for one US cup of icing sugar. That's the figure you'll find in our calculator and conversion tables.
If you're following an American recipe, you might see it called powdered sugar or confectioners' sugar. Both names generally mean the same thing as ordinary icing sugar in the UK.
You might also find recipes that use 120g per cup instead. We'll explain why the figures differ, but 113g is our standard when a recipe doesn't provide its own weight.
Icing sugar cups to grams: quick conversion table
Here are the quantities you'll need for common American recipes.
| US cups | Icing sugar |
|---|---|
| ¼ cup | 28g |
| ⅓ cup | 38g |
| ½ cup | 57g |
| ¾ cup | 85g |
| 1 cup | 113g |
| 1½ cups | 170g |
| 2 cups | 226g |
These figures are rounded to the nearest gram and assume ordinary icing sugar that hasn't been sifted before measuring.
A standard US cup holds about 237ml, slightly less than a 250ml metric cup.
If your recipe gives a weight in grams, follow that first. Otherwise, our table provides a practical starting point.
Is American powdered sugar the same as UK icing sugar?
Yes. For most recipes, ordinary UK icing sugar is exactly what you need.
American recipes commonly call it powdered sugar or confectioners' sugar. You don't need to look for a special American product in the supermarket.
Icing sugar is ordinary sugar ground into a very fine powder. That fine texture allows it to mix smoothly into buttercream, glazes and other icings.
Different brands may contain small amounts of ingredients that help prevent clumping. Some use maize starch (cornflour), while others use a different anti-caking agent.
For everyday baking, ordinary icing sugar is generally suitable for American recipes calling for powdered or confectioners' sugar.
Why do some recipes say 120g instead of 113g?
Because a cup measures volume, not weight, and powdered ingredients don't always settle into a measuring cup in the same way.
Icing sugar can be fluffy, compacted or slightly lumpy. Spooning it gently into a cup may give a different result from scooping and pressing it down.
Different baking references also use slightly different conventions. Some use 113g for a cup, while others use 120g. You may also see separate figures for sifted icing sugar.
Neither figure is necessarily wrong.
At Cupstograms, we've chosen 113g per US cup as our consistent reference. It means you'll get the same answer whether you use our calculator or one of our conversion tables.
But if an American recipe tells you that one cup of powdered sugar weighs 120g, use the recipe's own figure. That's the best indication of the amount its author intended.
Does it matter if I sift the icing sugar?
Sifting doesn't change the weight of sugar you've already measured, but it can change how much fits into a cup.
Icing sugar can develop small lumps, particularly after being stored for a while. Passing it through a sieve breaks those up, which is helpful when you want smooth buttercream or a glaze.
The order matters when you're measuring by volume.
If a recipe says “1 cup powdered sugar, sifted”, that generally means measure one cup first, then sift it.
If it says “1 cup sifted powdered sugar”, that generally means sift the sugar first, then measure one cup.
If you're weighing the sugar in grams, the process is simpler. Weigh the amount required, then sift it if the recipe asks you to.
Our 113g conversion assumes ordinary, unsifted icing sugar. Don't treat it as a separate measurement for every possible preparation method.
Can I use caster sugar instead of icing sugar?
Not usually for buttercream, glacé icing or dusting cakes.
Caster sugar is finer than ordinary granulated sugar, but it still consists of small crystals. Icing sugar is ground into a much finer powder.
If you use caster sugar in a mixture that isn't heated, those crystals may not dissolve properly, leaving a grainy texture.
The weights are different too. In our converter:
- One US cup of icing sugar is 113g.
- One US cup of granulated sugar is 198g.
So substituting the same number of cups would also change the amount of sugar considerably.
For a recipe that specifically calls for powdered sugar, ordinary icing sugar is normally the better choice.
Is royal icing sugar the same as ordinary icing sugar?
No. Check the packet before substituting it.
Ordinary icing sugar is the powdered sugar used in buttercream, simple glazes and many other recipes.
Some products sold as royal icing sugar are specially prepared mixes containing additional ingredients, such as dried egg white. They're intended for making royal icing, which sets firm and is often used for decorating biscuits and cakes.
If your American recipe simply says powdered sugar, buy ordinary icing sugar rather than assuming a royal icing mix is interchangeable.
Where our figures come from
Cupstograms uses 113g per US cup for ordinary, unsifted icing sugar. It's the consistent figure used in our ingredient data and calculators.
Our research includes:
- King Arthur Baking's ingredient weight chart (opens in a new tab) and Quaker Oats' measuring guide (opens in a new tab), which both support the 113g reference.
- Sally's Baking measuring guide (opens in a new tab), which uses 120g as its ordinary cup reference and gives a different figure for sifted sugar.
- BBC Good Food's sugar guide (opens in a new tab), which explains the different types of sugar and their uses.
- Silver Spoon's royal icing guidance (opens in a new tab), which helps distinguish ordinary icing sugar from royal icing products.
For other amounts, open our Cups to Grams converter and select Icing sugar.
The important thing to remember: American powdered sugar is generally ordinary icing sugar. If your recipe only gives cups, Cupstograms uses 113g per US cup. If the recipe supplies grams, follow those instead.