How many grams in a cup of cornstarch?

1 cup of cornstarch weighs 128 g by USDA's figure. King Arthur Baking lists 28 g per quarter cup, which is 112 g per cup.

Sources: USDA FoodData Central, King Arthur Baking ingredient weight chart · Checked October 10, 2026

Amount

Unit

128 g 4.5 oz

Sources range from 112 g to 128 g for 1 cup.

Converting a whole recipe?

Sous Chef converts every ingredient in a recipe to grams and millilitres in one tap, rounded to amounts you would actually weigh.

Cornstarch cups to grams table

Using 128 g per US cup. A US cup is 236.6 mL; 1 cup is 16 tablespoons.

Cornstarch cups to grams
US cups	Grams	Ounces	Tablespoons
⅛ cup	16 g	0.6 oz	2
¼ cup	32 g	1.1 oz	4
⅓ cup	43 g	1.5 oz	5.3
½ cup	64 g	2.3 oz	8
⅔ cup	85 g	3 oz	10.7
¾ cup	96 g	3.4 oz	12
1 cup	128 g	4.5 oz	16
1½ cups	192 g	6.8 oz	24
2 cups	256 g	9 oz	32
3 cups	384 g	13.5 oz	48
4 cups	512 g	18.1 oz	64

Why sources disagree

Cornstarch is a very fine powder that settles and packs in the box, so a cup can vary a lot. The sources are 16 g apart per cup. Most recipes use it by the tablespoon, where the difference is about a gram.

Source	Listed as	Grams per cup
USDA FoodData Central Cornstarch	1 cup = 128 g	128 g
King Arthur Baking ingredient weight chart Cornstarch	¼ cup = 28 g	112 g

Bold row is the figure the calculator uses. Figures listed for a smaller measure are multiplied up to one cup.

How to measure cornstarch accurately

Spoon cornstarch into the measure and level it, because tapping or packing changes the amount.
Weigh on a digital scale when you can, since cup scoops vary from cook to cook.
If you use cups, fill the same way every time so your results stay consistent.

Convert the whole recipe, not one line

Converting a recipe one ingredient at a time is where mistakes slip in. Sous Chef imports a recipe from a link or pasted text, then converts every ingredient at once: dry ingredients and butter to grams, liquids to millilitres. Tap again to go back to cups.

US recipe

2¼ cups all-purpose flour
1 cup butter, softened
¾ cup brown sugar, packed
1½ cups milk

In Sous Chef, after "Convert to metric"

275 g all-purpose flour
225 g butter, softened
170 g brown sugar, packed
350 ml milk

Example output. Sous Chef rounds to amounts you would actually weigh, so its numbers can differ by a few grams from the table above.

Common questions

How many grams is half a cup of cornstarch?

Half a cup of cornstarch is about 64 g, using 128 g per cup.

How many grams is 1 tablespoon of cornstarch?

1 tablespoon of cornstarch is about 8 g, since 1 cup is 16 tablespoons and 128 g per cup divided by 16 is 8 g.

More conversions

Cook in grams without doing the math.

Import any recipe and Sous Chef converts it, scales it, or swaps an ingredient for you. Free to download on iPhone.