Cornstarch in grams, and the two powders it gets confused with
Cornstarch weighs 128 grams to the US cup. The harder problem is not the number: it is that Australian cornflour is usually wheat starch, Japanese katakuriko is potato starch, and English recipe pages translate all three into the same word. Only the American entry means what an American recipe means.
Three powders, three countries, one word
Cornstarch in an American kitchen is corn. In Australia the packet on the shelf says cornflour, and it is usually wheaten cornflour, starch extracted from wheat rather than maize; Australian charts print a separate maize flour row beside it. In Japan the fine white thickener most recipes reach for is 片栗粉, katakuriko, which is potato starch. All three thicken a sauce, so a cook swapping between them often gets away with it. The weights do not swap so cleanly.
Cornstarch conversions in full
Following the USDA's 128 gram cup. A cup of cornstarch in grams, and two cups for a larger batch, both follow from it, though most recipes want a tablespoon or two.
| Cornstarch | Grams | Ounces |
|---|---|---|
| 1 tablespoon | 8 g | 0.28 oz |
| 1/4 cup | 32 g | 1.1 oz |
| 1/3 cup | 42.7 g | 1.5 oz |
| 1/2 cup | 64 g | 2.3 oz |
| 3/4 cup | 96 g | 3.4 oz |
| 1 cup | 128 g | 4.5 oz |
Density used: 0.54 g per ml.
The quarter cup that costs the most to multiply
Every master on this site refuses to scale a published fraction into a whole cup. Cornstarch is where that rule pays best. King Arthur measures a quarter cup at 28 g. Multiply by four and you get 112 g, against the 128 g the USDA weighed: 16 grams missing, an eighth of the cup and 13 percent of what the recipe asked for. That is the widest scaling error in our data, ahead of olive oil at 16 grams on a heavier cup. A powder settles as it fills, so the fourth quarter of a cup is not the first quarter repeated. The methodology page works through where the rule came from.
Katakuriko is not cornstarch
Both Japanese standard tables carry cornstarch and potato starch as separate rows, so we can read the gap directly rather than infer it. Benricho weighs コーンスターチ at 100 g per 200 millilitre cup and 片栗粉 at 130. Kyoritsu reads 90 and 110 for the same pair. Whichever table you take, the potato starch runs about a third heavier than the cornstarch printed beside it. An English page that translates 片栗粉 as cornstarch hands you that third as a silent error, and a thickener overshooting by a third is the difference between a sauce and a paste.
| Japanese table | Cornstarch | Katakuriko |
|---|---|---|
| Benricho | 100 g | 130 g |
| Kyoritsu Foods | 90 g | 110 g |
The metric cup we refuse to print
Other masters here carry a metric cup. This one does not, and the blank is the point. Australian Women's Weekly prints cornflour at 150 g and maize flour at 180 g as two rows with no note explaining the split. Since Australian cornflour is usually wheat starch, filing that 150 under our American heading would put an American label on an Australian product, and a reader would have no way to tell. We would rather leave the row empty and say why than fill it with a number that reads as an answer.
Questions about cornstarch weight
- How many grams is a cup of cornstarch?
- 128 g, from the USDA, the only authority publishing a whole cup. King Arthur measures a quarter cup at 28 g, and we do not multiply that by four: doing so gives 112, leaving 16 g of the measured cup unaccounted for.
- Is Australian cornflour the same as cornstarch?
- Often not. In Australia cornflour usually means wheaten cornflour, which is wheat starch rather than corn. It thickens in a similar way but it is a different product with different gluten content, and a chart labelled cornflour may be weighing either one.
- Is katakuriko the same as cornstarch?
- No. 片栗粉 is potato starch, and the Japanese tables weigh it at 110 to 130 g per 200 ml cup against 90 to 100 for cornstarch in the same tables. English recipe translations often print cornstarch for it, importing about a third more weight than intended.
Sources
USDA FoodData Central SR Legacy for the 128 gram cup. King Arthur Baking for the 28 gram quarter cup. The Kagawa Nutrition University standard tables, as reproduced by Benricho, and Kyoritsu Foods for the Japanese cornstarch and katakuriko rows. Australian Women's Weekly for the cornflour and maize flour rows we declined to publish. Full citations on the sources page.