Powdered sugar grams to cups
To convert grams to cups, divide the grams by 120. For example, 100 g of powdered sugar ≈ 0.83 cup.
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Powdered sugar is the trickiest sugar to measure by volume because it traps air and clumps. One US cup of unsifted powdered sugar weighs 120 grams. Sift it first and the same cup drops to roughly 110 grams, which is exactly why recipes specify "sifted" or "unsifted."
Powdered sugar grams to cups chart (US cup)
| Grams | Cups (approx.) | Decimal cups |
|---|---|---|
| 25 g | 0.21 cup | 0.21 |
| 50 g | 0.42 cup | 0.42 |
| 75 g | 0.62 cup | 0.62 |
| 100 g | 0.83 cup | 0.83 |
| 125 g | 1 cup | 1.04 |
| 150 g | 1¼ cups | 1.25 |
| 175 g | 1.46 cups | 1.46 |
| 200 g | 1⅔ cups | 1.67 |
| 250 g | 2.08 cups | 2.08 |
| 300 g | 2½ cups | 2.5 |
| 400 g | 3⅓ cups | 3.33 |
| 500 g | 4.17 cups | 4.17 |
Why powdered sugar weighs what it does
Powdered sugar is granulated sugar milled to a fine dust, then cut with about 3% cornstarch to stop caking. That starch and the huge amount of trapped air make it far lighter per cup than granulated sugar, even though both are pure sucrose by weight. The same 120-gram cup can read 110 to 125 grams depending on whether you sift, how the box settled in shipping, and the brand's grind (Domino and C&H run slightly different). Humidity matters too, since the cornstarch absorbs moisture and the sugar compacts.
How to measure powdered sugar
Never scoop the cup straight through the box, the fine powder compacts and you can grab 20 to 30 grams too much. Spoon it loosely into the cup and sweep level with a knife. If the recipe says "sifted," sift before measuring, not after, since sifting can change the volume by 10 percent or more. For glazes and royal icing, weighing in grams removes the guesswork entirely.
Common mistake
Treating "1 cup sifted" and "1 cup, then sifted" as the same thing. They are not. Sifting before measuring aerates the sugar so a cup weighs around 110 grams, while measuring first and sifting after gives you the full 120 grams. That 10-gram gap can make a glaze too thin or a frosting too stiff.
Other cup sizes
| Cup type | 1 cup of powdered sugar |
|---|---|
| US cup (240 ml) | 120 g |
| Metric cup (250 ml) | 125 g |
| Australian / South African cup (250 ml) | 125 g |
| Imperial cup (284 ml) | 142 g |
Where it matters
Powdered sugar dissolves instantly, so it is the backbone of glazes, royal icing, American buttercream, dusting finishes, and no-bake fillings. Precision matters most in icings and frostings, where a slightly heavy cup turns a pourable glaze into a paste, or stiffens buttercream past the point you can pipe it cleanly.
FAQ
How many grams is 1 cup of powdered sugar?
One US cup of unsifted powdered sugar is 120 grams, measured by spooning it loosely into the cup and leveling. If you sift it first, the same cup weighs closer to 110 grams.
Does powdered sugar weigh the same as granulated sugar?
By weight they are nearly identical sugar, but by volume they are very different. A cup of granulated sugar is about 200 grams, while a cup of powdered sugar is only 120 grams because it is full of air and cornstarch.
Should I sift powdered sugar before or after measuring?
Follow the recipe wording. "1 cup sifted" means sift first, then measure (about 110 grams). "1 cup, sifted" means measure 120 grams, then sift. When in doubt, weigh in grams.
Why is my powdered sugar lumpy?
The cornstarch added to prevent caking absorbs moisture from the air, forming lumps over time. Sift it before using in glazes or royal icing so you don't get gritty specks in a smooth finish.