Ran out of cornstarch mid-recipe? All-purpose flour will do the job at 1 tbsp cornstarch per 2 tbsp flour (thickening) — but only if you also adjust for what the swap takes away or adds. Starches are the quiet workhorses of the kitchen: a spoonful turns a thin liquid into a glossy sauce, holds a pie filling together, or lightens a cake crumb. Most of them swap one-to-one for thickening, but they do not all behave the same way once heated — some need a rolling boil to activate, some turn cloudy, some go slack if you boil them too long, and one of them (flour) needs twice as much and a longer cook to lose its raw taste. This page gives the ratio, shows it in a table, and walks through three real dishes so you can see the swap working in a pan, not just on paper.
The ratio, in a table
The table below converts cornstarch to all-purpose flour for the amounts you are most likely to meet. The rule is always the same: 1 tbsp cornstarch per 2 tbsp flour (thickening).
| Cornstarch called for | All-purpose flour to use |
|---|---|
| 1 tbsp | 1/2 tbsp |
| 2 tbsp | 1 tbsp |
| 3 tbsp | 1 1/2 tbsp |
| 1/4 cup | 2 tbsp |
| 1/3 cup | 2 tbsp + 2 tsp |
| 1/2 cup | 1/4 cup |
By weight, one cup of cornstarch is about 112 g (spooned and levelled, King Arthur Baking) and one cup of all-purpose flour is about 120 g (spooned and levelled, King Arthur Baking). The two weigh very differently per cup, so measure this swap by volume, not by weight, unless you are converting the whole recipe to grams — and then use the numbers above. All weights on this page are approximate; verify with a kitchen scale when the result matters.
Worked examples
Example 1: Beef gravy
A recipe for beef gravy calls for 2 tbsp of cornstarch to thicken the pan juices. Using the ratio, that becomes 4 tbsp of flour — twice as much. Whisk the flour into the hot fat first to make a roux, then add the stock gradually and simmer for several minutes, stirring, until the raw flour taste is gone. The gravy will be opaque and hearty rather than glossy and clear, which suits a beef gravy well.
Example 2: Chicken stew
A recipe for a chicken stew calls for 1 tbsp of cornstarch to thicken the cooking liquid. Using the ratio, that becomes 2 tbsp of flour. Stir the flour into a little cold water to make a slurry, add it to the simmering stew, and cook for at least five minutes so the flour loses its raw taste. The stew will be thicker and more opaque, with a richer, more rustic body.
Example 3: Cream soup
A recipe for a cream soup calls for 3 tbsp of cornstarch. Using the ratio, that becomes 6 tbsp of flour. Cook the flour in the butter at the start of the recipe, before adding the liquid, so it has time to cook through. The soup will be velvety and opaque — a classic cream soup texture, and a good use for this swap.
What changes in the result
Flour in place of cornstarch needs twice as much, and it changes the sauce in two ways: it makes it cloudier, and it needs a longer cook to lose its raw taste. Cornstarch thickens powerfully and leaves a clear, glossy sauce; flour thickens more gently, it turns the sauce opaque, and it must be cooked for several minutes or the sauce will taste of raw flour. The swap works well in a hearty gravy or a stew, where the opacity does not matter and the longer cook is part of the recipe anyway — and it is a poor swap for a clear sauce, where the cloudiness will show. Use twice the amount, cook it longer, and taste before serving.
When not to substitute
Do not use flour to thicken a clear sauce — it turns cloudy, and the difference will show in a fruit sauce, a clear glaze or a delicate consommé. Do not use it in a sauce that must be gluten-free either: flour contains gluten, while cornstarch does not. And do not use it where the sauce must thicken quickly: flour needs several minutes of cooking to lose its raw taste and reach its full thickness, so a last-minute slurry will not work the way a cornstarch slurry does.
Practical guidance
Always mix a starch into a little cold liquid before it meets anything hot — a slurry made with cold water, stock or milk is the single best defence against lumps. Add the slurry to a simmering liquid, stir constantly, and give it a full minute at a gentle bubble so the starch granules swell and the sauce reaches its final thickness; a sauce thickened with starch will look thinner while it is still hot than it will be on the plate. Do not boil a starch-thickened sauce hard for a long time: most starches thin out again if they are overheated or stirred too vigorously. If you are thickening something acidic, such as a fruit filling or a tomato sauce, add the starch late and keep the heat moderate, because acid weakens starch gels. Store starches in airtight jars in a cool, dry cupboard; they keep almost indefinitely. All amounts on this page are approximate; weigh the starch on a kitchen scale when the sauce or filling must set exactly.
Frequently asked questions
How much flour do I use instead of 1 tbsp of cornstarch?
Use 2 tbsp — the ratio is 1 tbsp of cornstarch per 2 tbsp of flour, so flour needs twice as much. One cup of cornstarch is about 112 g and one cup of all-purpose flour is about 120 g, so the weights are close, but measure by volume for this swap.
Will the sauce be cloudy?
Yes. Flour turns a sauce opaque, while cornstarch leaves it clear and glossy. That makes flour a good choice for a hearty gravy or stew, and a poor one for a clear fruit sauce or a delicate consommé.
Does flour need longer cooking?
It does — flour must be cooked for several minutes or the sauce will taste of raw flour. Stir it into the hot fat first to make a roux, or mix it into cold water and simmer the sauce for at least five minutes after adding it.
Can I use flour in a gluten-free sauce?
No — flour contains gluten, while cornstarch does not. If the dish must be gluten-free, use tapioca flour, arrowroot or potato starch instead.
Can I add flour at the end like cornstarch?
Not quite. A cornstarch slurry thickens a sauce in a minute; a flour slurry needs several minutes of cooking to lose its raw taste and reach its full thickness. Add it earlier, and give it time.
Scaling the swap up or down
A starch swap scales linearly: multiply both sides of the ratio by the same factor and the thickening power stays the same, whether you are thickening a single pan of gravy or a large pot of soup. The thing to watch is the slurry. Do not make one giant slurry for a very large pot — make it in two batches, so it stays smooth and lump-free, and add it in stages, stirring and waiting a minute between additions, because a starch-thickened sauce keeps thickening for a minute after the slurry goes in. If you add the whole amount at once to a big pot, you can overshoot and end up with a sauce that is too thick to pour. For a very small amount, measure the starch with measuring spoons rather than by eye: half a teaspoon too much in a single serving is a bigger error than a tablespoon too much in a large pot. All amounts on this page are approximate; weigh the starch on a kitchen scale when the sauce or filling must set exactly.
If the swap goes wrong — and how to store the substitute
If the sauce tastes of raw flour or raw starch, it was not cooked long enough — flour needs several minutes of cooking, and even a pure starch needs a full minute at a simmer, so give it time and taste before serving. If the sauce turns cloudy when it should be clear, the wrong starch was used: flour and cornstarch cloud a sauce, while arrowroot and tapioca stay clear, so choose the starch for the finish you want. If a fruit filling leaks in the oven, the starch did not get hot enough to set — bake until the filling bubbles in the middle, not just at the edges. Keep starches sealed and dry, and label the jar, because several white starches look identical.