Ingredient Weight Converter · starch
Cornstarch: cups to grams
1 cup of cornstarch weighs 120 grams. Use the converter below for any other amount, or check the quick-reference table.
By Andrew Flores, Editor and publisher, Nathan Management. Last reviewed .
Density source: USDA FoodData Central, cross-checked against the King Arthur Baking weight chart. How these figures are derived and corrected is documented in our editorial standards.
Cornstarch baseline: 1 cup = 120 g.
Common amounts
| Cups | Tablespoons | Grams | Ounces (weight) | Milliliters |
|---|---|---|---|---|
| 1/4 cup | 4.0 | 30 g | 1.06 oz | 59 mL |
| 1/3 cup | 5.3 | 40 g | 1.41 oz | 79 mL |
| 1/2 cup | 8.0 | 60 g | 2.12 oz | 118 mL |
| 2/3 cup | 10.7 | 80 g | 2.82 oz | 158 mL |
| 3/4 cup | 12.0 | 90 g | 3.17 oz | 177 mL |
| 1 cup | 16.0 | 120 g | 4.23 oz | 237 mL |
| 1.5 cups | 24.0 | 180 g | 6.35 oz | 355 mL |
| 2 cups | 32.0 | 240 g | 8.47 oz | 473 mL |
| 3 cups | 48.0 | 360 g | 12.70 oz | 710 mL |
| 4 cups | 64.0 | 480 g | 16.93 oz | 946 mL |
Spoon weights
Derived from the same 120 g per cup — a US tablespoon is 1/16 of a cup and a teaspoon is 1/48.
| Amount | Grams |
|---|---|
| 1 tablespoon | 7.5 g |
| 1 teaspoon | 2.5 g |
| 1/2 teaspoon | 1.3 g |
| 1/4 teaspoon | 0.63 g |
Cornstarch at a glance
- Working dose
- 1 tablespoon (about 7.5 g) per cup of liquid for gravy; 2 tablespoons for a pie filling that holds a cut
- Slurry ratio
- 1 part cornstarch to 2 parts cold liquid
- Breaks down with
- hard boiling, long simmering, and acid (lemon, vinegar, tomato)
What a cup of cornstarch actually weighs
The published 120 g assumes one specific way of filling the cup. Here is what the same cup weighs under the other common handling methods and product forms, and how far off the recipe you end up.
| How it was measured | Grams per cup | vs. published | Why |
|---|---|---|---|
| Spooned and leveled | 120 g | published figure | The published figure. In practice you will measure this by the tablespoon, not the cup. |
| Scooped and tapped | ~135 g | +13% | Cornstarch is a fine powder and compacts like flour when the cup plows through the box. |
A tilde (~) marks a working estimate rather than a published figure — it varies with brand, grind, or how hard the cup was packed.
Why measuring cornstarch by cup goes wrong
Cornstarch is pure starch, no protein, no fiber. It thickens as the granules swell and gelatinize — starting around 145 °F and reaching full thickening near the boil — and it loses thickening power if boiled hard for more than a minute after that. A cup weighs about 120 grams — coincidentally the same as AP flour, which is why some old recipes treat them as interchangeable thickeners despite the very different behavior.
Practical tips for working with cornstarch
To thicken a sauce, mix cornstarch with cold water in a ratio of one part cornstarch to two parts water (a 'slurry') before whisking it into hot liquid. Adding dry cornstarch directly creates lumps that no amount of whisking will remove. One tablespoon thickens about one cup of liquid to gravy consistency; two tablespoons gives you a pie filling that holds a cut.
Note from this ingredient's record: Used as a thickener. One tablespoon of cornstarch (8 g) thickens about one cup of liquid to a gravy consistency.
Substitutions that work — and what they cost you
All-purpose flour as a thickener
Ratio: 2 tablespoons flour = 1 tablespoon cornstarch
Trade-off: Cloudy rather than glossy, and it tastes raw unless you cook it a few minutes. It survives long simmering better than cornstarch does.
Arrowroot
Ratio: 1:1
Trade-off: Clearer and glossier, and it survives freezing where cornstarch weeps. It breaks down in dairy and cannot take prolonged heat.
Tapioca starch
Ratio: About 2 tablespoons tapioca = 1 tablespoon cornstarch
Trade-off: Stringy in a savoury sauce, excellent in fruit pies where you want a glossy set that tolerates freezing.
When cornstarch ruins the recipe
| What you see | What went wrong | What to do |
|---|---|---|
| Sauce is full of gelatinous lumps | Dry cornstarch hit hot liquid; the outside of each clump gelatinized and sealed the dry centre. | Always slurry first — 1 part starch to 2 parts cold liquid — then stream it into the hot pot while whisking. |
| Sauce thickened, then went thin again | It was boiled hard or held too long, or an acidic ingredient broke the starch chains. | Bring it just to a simmer for under a minute, then pull it. Add lemon juice or vinegar at the very end. |
Storing cornstarch
Sealed and dry, cornstarch keeps effectively forever. It absorbs odours, so keep it away from the spice shelf.
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