Powdered sugar

One US cup of powdered sugar weighs 120 grams (4.2 ounces), measured unsifted, spooned into the cup. Going the other way, 100 grams is about 0.83 cups.

Also called confectioners' sugar, icing sugar, 10X sugar.

Sugars compared: cup weights side by side, the source behind each, and why they differ.

The first entry where USDA names the measuring method itself rather than recording an undetermined cup. FDC 169656 publishes a sifted cup at 100 g (0.4227 g/ml) and an unsifted cup at 120 g (0.5072 g/ml), a difference of 20%. That is a real difference between two ways of filling the cup, not a disagreement about one quantity, so the entry splits into two states, sifted and unsifted.

Powdered sugar behaves this way because it is not a crystal like granulated sugar but a milled powder cut with about 3% cornstarch to stop it caking, and milled powders clump and bridge. Sifting breaks the clumps and traps air. This is why recipes specify sifted or unsifted for powdered sugar and rarely bother for granulated.

USDA's own figures support the split internally: their unsifted teaspoon at 2.5 g gives 0.5072 g/ml, identical to the unsifted cup, so those two are one density rounded twice rather than two measurements. Their unsifted tablespoon at 8 g gives 0.5410 g/ml, 6.7% above the other two; 8 g is a whole number on a 14.8 ml spoon and the rounding band is wider than the difference being measured, so it is not used. The unsifted state publishes USDA's 120 g per cup.

King Arthur's chart gives an unsifted cup at 113 g, or 0.4776 g/ml, 6.2% below it. Both sources name the same state, so the gap is not a difference of method; it is the ordinary variability of measuring a milled powder, which is why this entry sits in the milled category at a 10% tolerance rather than the 5% that suits crystalline sugar. The larger measure is published under the usual preference, and King Arthur's figure stands beside it rather than being averaged in.

The sifted state has USDA alone, so it publishes no single figure of its own, though the page shows what USDA measured. No standards body publishes a density for milled sugar, so the Codex route that resolved olive oil is not available. Two independent sources support the published state, which is enough to publish; confidence stays medium until a third independent measurement confirms it.