Why sifting changes the weight
Powdered (confectioners') sugar is granulated sugar ground into an extremely fine powder, then blended with a small amount of cornstarch to keep it from clumping. Straight from the bag, it settles and compacts somewhat — a cup measured by scooping and leveling weighs about 120g. Sifting breaks up any compacted clumps and folds air into the powder, so the same volume holds noticeably less sugar afterward — closer to 100g per cup. A recipe that says "1 cup powdered sugar, sifted" is expecting you to sift first and then measure, which gives a different (lighter) result than measuring first and sifting after.
Getting the right glaze or icing consistency
Most of the time powdered sugar is measured for icing or glaze, where the real goal is a texture, not a precise gram figure — so it helps to know the rough sugar-to-liquid ratios for each consistency and adjust with small additions from there:
| Consistency | Powdered sugar | Liquid (milk/water) |
|---|---|---|
| Thin drizzle glaze | 1 cup | 3–4 Tbsp |
| Spreadable icing | 1 cup | 1½–2 Tbsp |
| Thick piping/writing icing | 1 cup | 1 Tbsp or less |
Add liquid a teaspoon at a time once you're close — powdered sugar mixtures thicken up quickly near the end, and it's much easier to loosen a too-thick glaze than to rescue one that's gone runny.
No powdered sugar? Make your own
Blend 1 cup granulated sugar with 1 tablespoon cornstarch in a blender or food processor on high for about a minute, until it's a fine, uniform powder — the cornstarch mimics the anti-caking role it plays in store-bought powdered sugar. This works fine for glazes and dusting but can leave a very slight graininess compared to commercial powdered sugar, since home blenders can't grind quite as fine.
Quick reference chart
| Cups | Unsifted | Sifted |
|---|---|---|
| ¼ cup | 30g | 25g |
| ½ cup | 60g | 50g |
| 1 cup | 120g | 100g |
| 2 cups | 240g | 200g |
FAQ
Does a recipe assume sifted or unsifted unless it says? Assume unsifted unless the recipe explicitly says "sifted" — most modern recipes are written for sugar measured straight from the bag.
Can I skip sifting if my powdered sugar looks clump-free? For glazes and icings, usually yes. For delicate baked goods where powdered sugar is a major dry ingredient (some shortbreads, meringue-based cookies), sifting still helps distribute it evenly even without visible clumps.