Powdered Sugar Weighs Half of Granulated (By Cup)

A recipe calls for 1 cup of sugar. You only have powdered sugar in the cabinet. You shrug and pour. The cookies come out flat and not sweet enough. The cup looked the same, but the math was not.

Why the same cup weighs so differently

Granulated sugar has uniform, dense crystals. They pack tightly into the cup. Powdered sugar is granulated sugar ground into a fine dust, then mixed with 3 percent cornstarch to keep it from clumping. The fine powder traps a lot of air. A cup of fluff weighs less than a cup of crystals.

When the swap is possible (and when it is not)

By weight: yes, sometimes

If you weigh, you can swap powdered for granulated by weight in some recipes. Frostings, glazes, and dustings expect powdered. Cakes and cookies expect granulated for structure. The sugar does different jobs in each.

By volume: almost never

If you swap 1 cup of granulated for 1 cup of powdered, you just cut the sugar by 43 percent. The cookies will be drier and less sweet. Cookies and cakes need that sugar weight to spread, brown, and stay tender.

All three white sugars by the cup

• Granulated white sugar: 200 g per cup. The default for most baking.
• Powdered (confectioners') sugar: 113 g per cup. Used in frostings, glazes, royal icing, and as a dusting.
• Superfine (caster) sugar: about 195 g per cup. Sits between the two. Used in meringues and sponge cakes where it dissolves faster than granulated.

If your recipe says powdered and you only have granulated

Process granulated sugar in a clean coffee grinder or food processor for 30 seconds to make a rough powdered sugar. Add 1 teaspoon of cornstarch per cup to mimic the anti-caking. The texture is close but not exact; do not use for delicate icings.

If your recipe says granulated and you only have powdered

No clean swap. Powdered sugar has cornstarch in it, which changes the texture of cookies and cakes. Better to wait until you have the right sugar, or pick a different recipe that uses powdered sugar (like shortbread or Mexican wedding cookies).