Cornstarch vs Flour vs Arrowroot vs Tapioca: Thickener Conversions in Grams

How much cornstarch replaces flour (and the reverse), arrowroot and tapioca swaps, grams per tablespoon for each, and how much thickener a cup of liquid needs.

Flour, cornstarch, arrowroot and tapioca all thicken by the same trick — starch granules swell in hot liquid — but they do not do it with the same strength. Swapping one for another spoon for spoon is the most common reason a gravy ends up gluey or a pie filling ends up as soup.

Grams per tablespoon for each thickener

Thickener — Grams per cup — Grams per tablespoon — Grams per teaspoon

All-purpose flour — 125 g — about 7.8 g — about 2.6 g

Cornstarch — 128 g — about 8 g — about 2.7 g

Arrowroot powder — 128 g — about 8 g — about 2.7 g

Tapioca starch — 113 g — about 7.1 g — about 2.4 g

These come from the site's ingredient data (flour, cornstarch, arrowroot and tapioca), divided by 16 tablespoons per cup and 48 teaspoons per cup. A tablespoon of each weighs almost the same, which is exactly why the volume swap is misleading: the difference is in thickening power, not weight.

The swap ratios

To replace — Use instead

1 tbsp cornstarch (8 g) — 2 tbsp all-purpose flour (about 16 g)

1 tbsp cornstarch (8 g) — 1 tbsp arrowroot (8 g)

1 tbsp cornstarch (8 g) — 2 tbsp tapioca starch (about 14 g)

2 tbsp flour (about 16 g) — 1 tbsp cornstarch (8 g)

All-purpose flour is only around 70% starch — the rest is mostly protein, with some fibre and moisture — so it takes roughly twice as much to reach the same thickness. That is the source of the 2-to-1 rule.

How much thickener per cup of liquid

For one cup (about 240 ml) of stock, milk or juice:

Result — Flour — Cornstarch

Thin sauce or soup — 1 tbsp (about 8 g) — ½ tbsp (about 4 g)

Medium sauce or gravy — 2 tbsp (about 16 g) — 1 tbsp (about 8 g)

Thick sauce or pie filling — 3 tbsp (about 23 g) — 1½ tbsp (about 12 g)

Worked example: gravy for a roast. You have 3 cups of pan juices and stock and want a medium gravy. With flour: 3 × 2 tbsp = 6 tbsp, about 47 g. With cornstarch: 3 × 1 tbsp = 3 tbsp, about 24 g, mixed into about 6 tbsp of cold water first.

Worked example: converting a recipe the other way. A stew recipe says "¼ cup flour" to thicken, but you need it gluten-free. A quarter cup is 4 tbsp of flour, about 31 g. Replace it with 2 tbsp of cornstarch (16 g) or 2 tbsp of arrowroot (16 g).

How each one behaves

All-purpose flour gives an opaque, matte sauce and needs a few minutes of simmering to lose its raw taste. It is the most stable over long cooking and reheats well, which is why it is the classic choice for gravy and béchamel. Cook it in fat first (a roux) or whisk it into cold liquid to avoid lumps.

Cornstarch gives a glossy, translucent result and thickens quickly once the liquid comes to a boil — it needs a brief boil to reach full thickness. Stirring hard or boiling for a long time afterwards breaks it down and the sauce thins again. It also turns spongy and weeps after freezing, so it is a poor choice for dishes you plan to freeze.

Arrowroot thickens at a lower temperature than cornstarch and stays clear, which suits fruit sauces and glazes. It freezes better than cornstarch, but it thins if boiled for long and can go slimy in dairy-based sauces.

Tapioca starch sets glossy and slightly stretchy, holds up well in fruit pies and freezes well. Use about twice the volume of cornstarch.

Getting it smooth

Every starch clumps if it hits hot liquid dry. For cornstarch, arrowroot and tapioca, make a slurry: stir the starch into about twice its volume of cold water or stock until smooth, then whisk it into the simmering liquid. For flour, either make a roux (equal weights of flour and fat, cooked for a minute or two) or shake the flour with cold liquid in a closed jar.

Add the thickener a little at a time. A sauce thickens further as it cools, so stop when it is slightly thinner than you want it on the plate.

When to pick which

Gravy, stew, béchamel, anything reheated: flour.

Stir-fry sauces, custards, glossy pie fillings eaten fresh: cornstarch.

Fruit glazes, dishes you will freeze, quick sauces added at the end: arrowroot.

Fruit pies, especially frozen ones: tapioca.

For other amounts, the grams to tablespoons converter turns any weight of these starches into spoons, and the cornstarch page has a full cups-to-grams chart.

Frequently asked questions

How much cornstarch replaces 1 tablespoon of flour?

About ½ tablespoon (1½ teaspoons). Cornstarch is pure starch and has roughly twice the thickening power of all-purpose flour, so 2 tablespoons of flour (about 16 g) become 1 tablespoon of cornstarch (about 8 g).

How many grams is a tablespoon of cornstarch?

About 8 g, using USDA FoodData Central's 128 g per cup. A teaspoon is about 2.7 g. King Arthur Baking lists cornstarch a little lighter, at 112 g per cup (7 g per tablespoon).

Can I use arrowroot instead of cornstarch?

Yes, in the same amount by weight. Arrowroot thickens at a lower temperature and freezes better, but it can turn slimy in dairy sauces and thins out if boiled for long.

How much tapioca starch replaces cornstarch?

About twice as much by volume: 2 tablespoons of tapioca starch for every tablespoon of cornstarch. Tapioca gives a glossy, slightly stretchy set and is popular in fruit pies.

How much cornstarch do I need to thicken 1 cup of liquid?

About 1 tablespoon (8 g) for a medium sauce or gravy, mixed first into 2 tablespoons of cold liquid. With flour you need about 2 tablespoons (16 g) for the same thickness.