1 cup of cornstarch in grams — 120 g.

Why 120 g per cup

Cornstarch's grain is fine and uniform, so it packs to about the same density as all-purpose flour: 120 g/cup. Recipes usually call for it by the tablespoon (8 g).

Flour is the trickiest ingredient to measure by volume. A cup of all-purpose flour can weigh anywhere from 113 g (gently spooned) to 150 g (scooped and packed) — a 30 % spread that's the difference between a tender cake and a tough one. The canonical 120 g/cup figure used here matches King Arthur Baking's reference, which assumes the spoon-and-level method: fluff the flour in its container, spoon it gently into the measuring cup, and level the top with a straight edge. Any time a recipe matters, weigh.

Common kitchen applications for cornstarch

Cornstarch is the most common thickener for sauces, fruit pie fillings, custards, and Asian-style stir-fry glazes. Always mix with cold liquid first (a slurry) before adding to hot liquid to prevent lumping. Loses thickening power if boiled too long or held under prolonged acid heat — for acidic sauces, arrowroot is the more reliable substitute.

The most accurate way to measure cornstarch

For recipes where the outcome matters — bakes, doughs, anything leavened — measure cornstarch on a kitchen scale set to grams. Set the bowl on the scale, press tare to zero, then add until the readout matches the gram value the recipe calls for. This removes the largest source of cup-to-cup variation: how you scoop.

The cup-based numbers on this page assume the “spoon and level” method — fluffing the ingredient in its container, spooning it into the cup, and levelling the top with a straight edge. Scooping directly with the cup packs more in, and can push the gram value up by 20-30 % for fluffy ingredients like flour and cocoa.