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Gravy Thickener Calculator

Calculate how much flour or cornstarch you need to thicken a given amount of gravy or sauce.

Result

Flour Needed
4 tbsp

For a roux, whisk equal parts flour and fat together and cook briefly before whisking in liquid. Flour needs a few minutes of simmering to lose its raw, pasty taste and fully activate its thickening power.

About the Gravy Thickener Calculator

The Gravy Thickener Calculator works out how much flour or cornstarch to whisk into a given volume of liquid to hit a thin, medium, or thick consistency, since the two thickeners need very different amounts to produce a similar result. Enter how many cups of gravy, pan sauce, or stock you are thickening, pick a thickener, and choose the consistency you are aiming for.

How It Works

Each thickener and consistency combination maps to a fixed tablespoon-per-cup rate: flour ranges from 1 tbsp per cup for thin up to 3 tbsp per cup for thick, while cornstarch ranges from 0.5 up to 1.5 tbsp per cup across the same three levels. The calculator multiplies your liquid volume by the rate for the combination you selected to return a total tablespoon amount.

Thickener (tbsp) = Liquid (cups) x Rate, where Rate in tbsp per cup for flour is 1 (thin), 2 (medium), or 3 (thick), and for cornstarch is 0.5 (thin), 1 (medium), or 1.5 (thick).

Formula & Methodology

By hand, first choose your thickener and target consistency, then look up its per-cup rate: medium-thickness flour gravy, for example, uses 2 tablespoons of flour per cup of liquid. Multiply that rate by your total liquid volume to get the total tablespoons needed. For a roux, that flour is first whisked with an equal amount of fat and cooked briefly before liquid is added; for a cornstarch slurry, the cornstarch is first mixed with an equal amount of cold water before going into the hot liquid, which prevents clumping.

Examples

Thickening a roast pan sauce

3 cups of liquid with flour at medium consistency uses the 2 tbsp-per-cup rate, for a total of 6 tablespoons of flour.

Thick cornstarch gravy for a smaller batch

2 cups of liquid with cornstarch at thick consistency uses the 1.5 tbsp-per-cup rate, for a total of 3 tablespoons of cornstarch.

Advantages

  • Converts a vague thin, medium, or thick preference into an exact tablespoon amount before you start cooking.
  • Lets you compare flour and cornstarch quantities side by side for the same batch of liquid.
  • Scales directly with liquid volume, so it works the same for a single cup of pan sauce or a large batch of holiday gravy.

Common Mistakes

  • Using the same tablespoon amount for cornstarch as for flour, which produces a gravy roughly twice as thick as intended.
  • Adding dry flour or cornstarch straight into hot liquid instead of first making a roux or a cold slurry, leading to lumps.
  • Judging thickness while the gravy is still hot, since both flour and cornstarch continue thickening slightly as the liquid cools.

Edge Cases to Watch For

  • Cornstarch rates are roughly half of the equivalent flour rates at every consistency level, reflecting cornstarch's higher thickening power per tablespoon as a nearly pure starch.
  • If an unrecognized thickener or consistency combination is ever submitted, the calculator falls back to a medium flour rate of 2 tbsp per cup.
  • Flour needs a few minutes of active simmering after it's added to lose its raw taste and reach full thickening power, while cornstarch thickens almost immediately once the liquid returns to a simmer, so the two aren't interchangeable in technique even at a matched tablespoon amount.

Common Use Cases

  • Home cooks converting a vague recipe instruction like thicken to taste into a specific starting amount.
  • Anyone substituting cornstarch for flour, or the reverse, in an existing gravy or sauce recipe.
  • Cooks scaling a gravy recipe up for a larger holiday gathering without guessing at the thickener amount.
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

Why does cornstarch thicken with about half as much as flour?

Cornstarch is nearly pure starch, giving it roughly twice the thickening power by volume compared to flour, which is only about 75% starch (the rest being protein and other components) - this is why recipes calling for cornstarch as a substitute for flour typically use about half the amount.

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Conclusion

Because flour and cornstarch thicken at different rates, matching the thickener to its own rate table avoids the trial and error of adding a little at a time. The result is a specific tablespoon target to start from, which can still be fine-tuned slightly once the gravy is simmering.