One cup of cornstarch weighs 112 grams when spooned and levelled, according to King Arthur Baking. That is a light, fine white powder — far lighter per cup than flour, which weighs 120 grams, and dramatically lighter than sugar at 198 grams. A single tablespoon of cornstarch weighs about 7 grams, and a teaspoon weighs about 2.3 grams. These are approximate figures, because a powder as fine as cornstarch settles and compacts easily, but 112 grams per cup is the reliable reference value, and you should verify with a kitchen scale whenever the amount matters — which, with a thickener as powerful as cornstarch, it almost always does.

Cornstarch is the quiet workhorse of the kitchen. It thickens sauces, gravies, soups and custards without adding flavour or colour; it lightens cakes when a spoonful replaces some of the flour; it keeps fried coatings crisp; and it stops powdered sugar from clumping. It is also unforgiving. The difference between a silky sauce and a gluey, starchy mess is often a single tablespoon, and the difference between a tablespoon and a tablespoon-and-a-half is only about 3.5 grams. That is why weighing cornstarch matters more than weighing almost any other dry ingredient in this guide: the amounts are small, the effect is large, and volume measures of a fine powder are the least reliable measures in the kitchen.

How much does cornstarch weigh?

The table below gives the weight of cornstarch for the amounts you are most likely to meet, from a single teaspoon up to four cups. All figures come from the King Arthur Baking value of 112 grams per cup, spooned and levelled. Because cornstarch is a fine powder, how you fill the cup matters enormously — a scooped cup, where you plunge the measure into the box, can weigh 130 grams or more, which is a 16 percent error. Spoon it in lightly and level it off, or better still, weigh it.

Amount Weight (grams) Weight (ounces)
1 teaspoon 2.3 g 0.08 oz
1 tablespoon 7 g 0.25 oz
1/4 cup 28 g 0.99 oz
1/3 cup 37 g 1.31 oz
1/2 cup 56 g 1.98 oz
2/3 cup 75 g 2.64 oz
3/4 cup 84 g 2.96 oz
1 cup 112 g 3.95 oz
1 1/2 cups 168 g 5.93 oz
2 cups 224 g 7.90 oz
3 cups 336 g 11.85 oz
4 cups 448 g 15.80 oz

A useful comparison: one cup of cornstarch weighs almost exactly half as much as one cup of granulated sugar (198 grams) and slightly less than one cup of all-purpose flour (120 grams). That lightness is the clue to its character — cornstarch is pure starch, with no protein, no fibre and no fat, milled to a powder so fine it feels like silk between your fingers. It packs down under its own weight, which is why a cup measured from the bottom of a half-empty box weighs more than a cup measured from a freshly opened one.

For everyday cooking, the tablespoon row is the one that matters. Most sauces are thickened with 1 to 2 tablespoons of cornstarch per cup of liquid, which is 7 to 14 grams. A tablespoon is a small amount to weigh — most home scales read to the nearest gram, so 7 grams will read cleanly — but it is also a small amount to measure by volume, and a heaped tablespoon can easily hold 10 or 11 grams. If your sauce keeps turning out thicker than the recipe promised, a heaped spoon is the usual suspect.

Worked examples

Example 1: Fixing a stir-fry sauce that always turns gluey

A stir-fry sauce recipe calls for 1 tablespoon of cornstarch mixed with 2 tablespoons of cold water to thicken 1 cup of sauce. You have always measured a heaped tablespoon, which holds about 10 grams instead of 7 — nearly 45 percent too much. The sauce sets like wallpaper paste instead of coating the vegetables in a glossy sheen. The fix is to weigh 7 grams on the scale, or to spoon the cornstarch into the tablespoon and level it with the back of a knife. Once you do, the same recipe produces the glossy, clinging sauce it was written to make. This is the single most common cornstarch mistake in home cooking, and it is entirely a measurement problem.

Example 2: Thickening a fruit pie filling

A cherry pie filling calls for 1/4 cup of cornstarch to thicken 4 cups of cherries and their juice — 28 grams. You are doubling the recipe for two pies, so you need 56 grams, or half a cup. If you scoop the cornstarch from the box instead of spooning it, you might get 65 grams per half cup, and the filling will set too firmly and taste starchy. Weighing 56 grams takes ten seconds and removes the guesswork. It also matters that you mix the cornstarch with a little of the cherry juice before adding it to the hot fruit: cornstarch dumped straight into hot liquid forms lumps that no amount of stirring will remove.

Example 3: Lightening a sponge cake

A sponge cake recipe replaces 2 tablespoons of the flour with 2 tablespoons of cornstarch to make the crumb more tender — 14 grams of cornstarch. This is a classic technique: cornstarch has no gluten, so swapping it in for some of the flour weakens the gluten network and produces a finer, softer cake. But the swap only works if the amount is right. Two heaped tablespoons (about 20 grams) will make the cake crumbly and dry; two level tablespoons (14 grams) will make it tender. Weigh the cornstarch, and weigh the flour you remove, and the technique works exactly as written.

Method and source

The figure of 112 grams per cup comes from King Arthur Baking's ingredient weight chart, measured spooned and levelled: the cornstarch is spooned lightly into the cup and the top is levelled off with a straight edge, without tapping, shaking or packing. King Arthur lists the value with high confidence, and it agrees with the values used by most professional baking references.

There is no serious dispute about this figure, but there is a serious warning attached to it: the method is everything. Cornstarch is one of the most compressible powders in the kitchen. A cup that is spooned and levelled weighs 112 grams; the same cup filled by scooping directly from the box can weigh 125 to 135 grams; a cup that has been tapped on the bench to settle it can weigh more still. That is a spread of more than 20 grams per cup — enough to turn a sauce from silky to stodgy. If a recipe was developed with weighed cornstarch, and most professional recipes are, then a scooped cup will overshoot every time. Weigh it, or spoon and level with discipline.

Cornstarch is also known as cornflour in the UK, Ireland, Australia and New Zealand — the same product, the same fine white starch. Do not confuse it with cornmeal, which is coarsely ground dried corn and weighs 138 grams per cup, or with corn flour in the American sense, which is finely ground whole corn. If a British recipe says "cornflour," it means the cornstarch on this page, and the 112-gram figure applies.

Practical guidance

Cornstarch thickens by gelatinisation: when its starch granules are heated in liquid to around 95°C, they swell and burst, trapping water and turning the liquid thick and glossy. That is why the rules for using it are so specific. Always mix cornstarch with a small amount of cold liquid first to make a slurry — about twice as much cold water as cornstarch by volume — and then stir the slurry into the hot liquid. Never add dry cornstarch to hot liquid, and never add it to a boiling sauce and walk away: it needs a full minute at a simmer to cook out its raw, starchy taste, and if you stop heating too early the sauce will taste of raw starch and thin out again as it cools.

Cornstarch-thickened sauces do not reheat well and do not freeze well. The gel breaks down on freezing and weeps liquid on thawing, so a cornstarch-thickened soup that was perfect on Tuesday will be thin and watery on Thursday. If you are cooking for the freezer, use flour or tapioca starch instead — tapioca freezes far better. Cornstarch also loses its thickening power in very acidic liquids and in sauces that are simmered for a long time, so for a long-cooked tomato sauce or a sharp lemon curd, add the cornstarch late and keep the cooking time short.

The most common mistakes, in order: using a heaped spoon instead of a level one; adding the powder dry to hot liquid and getting lumps; undercooking it so the sauce tastes starchy; and using it in a recipe that will be frozen. Storage is easy: cornstarch keeps indefinitely in an airtight container in a cool, dry place. It absorbs moisture from the air, so keep the box closed and do not store it above the stove. If it clumps, it has absorbed moisture — break the clumps up and use it anyway, or replace it if the clumps are hard.

Frequently asked questions

How many grams is 1 tablespoon of cornstarch?

One tablespoon of cornstarch weighs about 7 grams when levelled. A heaped tablespoon can hold 10 to 11 grams, which is why weighing is more reliable than spooning for this ingredient. Most sauces need 1 to 2 tablespoons (7 to 14 grams) per cup of liquid. If your sauce keeps coming out too thick, check whether your spoon is level.

How many grams is 1/4 cup of cornstarch?

One quarter cup of cornstarch weighs 28 grams, spooned and levelled. That is the amount typically used to thicken a fruit pie filling made with about 4 cups of fruit. If you are doubling a pie recipe, you need 56 grams (half a cup). Weigh it rather than scooping, because a scooped quarter cup can easily weigh 32 or 33 grams.

Is cornstarch the same as cornflour?

In the UK, Ireland, Australia and New Zealand, yes — "cornflour" is the name for the fine white starch sold as cornstarch in the United States. In the US, "corn flour" usually means finely ground whole corn, which is a different product. If you are following a British recipe that calls for cornflour, use cornstarch, and the 112-grams-per-cup figure on this page applies.

Why did my cornstarch sauce go lumpy?

Lumps happen when dry cornstarch hits hot liquid. The outside of each clump gelatinises instantly and seals the dry powder inside, and no amount of stirring will break it open. The fix is to always make a slurry first: mix the cornstarch with a little cold water until smooth, then stir the slurry into the hot liquid. If you already have lumps, strain the sauce through a fine sieve.

Can I substitute flour for cornstarch?

Yes, but the ratio is different: use twice as much flour as cornstarch by volume. One tablespoon of cornstarch is replaced by 2 tablespoons of flour. Flour also needs to be cooked longer to lose its raw taste, and it makes sauces opaque rather than glossy. For a glossy, clear sauce — a stir-fry glaze or a fruit pie filling — cornstarch is the better choice. For a gravy or a cream soup, flour works well.

Does cornstarch go bad?

Cornstarch does not spoil in the usual sense — it is pure starch with no fat to go rancid and no moisture to support mould, as long as it stays dry. Stored in an airtight container in a cool, dry place, it keeps indefinitely. If it absorbs moisture it will clump; break the clumps up and it is still usable, but if it smells musty or has been stored damp, replace it.

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