Roux and Sauce Thickening Calculator
Choose how thick you want the sauce and how much liquid you are thickening.
Answer
30g butter and 30g flour
The ratio
What to do
- 1Melt 30g butter over a medium heat.
- 2Stir in 30g plain flour and cook for 2 minutes, stirring.
- 3Add 500ml liquid gradually, beating smooth each time.
- 4Simmer gently for 5 minutes to cook out the flour and thicken fully.
Next step
Worth knowing
- Cheese sauce, lasagne, cauliflower cheese, coats the back of a spoon.
- A roux is always equal weights of butter and flour. Only the amount changes with how thick you want the sauce.
- Cook the flour and butter together for two minutes before any liquid goes in, or the sauce will taste of raw flour.
- Add the liquid a little at a time and beat smooth between each addition. Warm liquid is easier than cold.
Source: Classic sauce ratios as taught in standard UK cookery references · Reviewed 2026-09-10 · Guidance version 1.0.0
Reference and detail
Roux per 500ml of liquid
| Thickness | Per 500 ml | What it suits |
|---|---|---|
| Thin (pouring) | 20 g butter + 20 g flour | Soups, pouring sauces and gravies. |
| Medium (coating) | 30 g butter + 30 g flour | Cheese sauce, lasagne, cauliflower cheese, coats the back of a spoon. |
| Thick (binding) | 45 g butter + 45 g flour | Croquettes, fish pie bases and soufflé bases. |
| Very thick (panade) | 60 g butter + 60 g flour | Sets firm when cold. Used for croquettes you need to shape and crumb. |
Enter your own quantity above for the exact weights.
Equal butter and flour, every time
A roux is always equal weights of the two. Only the amount changes: more roux for the same liquid gives a thicker sauce.
Cook the flour before the liquid
Two minutes of stirring cooks out the raw flour taste and coats the starch in fat, which is what stops the sauce going lumpy when the liquid goes in.
Add liquid gradually and beat smooth
Splash by splash, beating between each addition, gives a glossy sauce with no lumps. Warm liquid is more forgiving than cold, but neither will fail if you go slowly.
Questions and answers
Questions about making a roux
What is the basic ratio for a roux?
Equal parts butter and flour by weight, cooked together before the liquid goes in. How much of each you need per 500ml of liquid depends on how thick you want the finished sauce. Enter your liquid volume and desired thickness above.
Why is my roux-based sauce too thick?
You have used more roux than the liquid needs for the thickness you wanted, or reduced the sauce for too long once the liquid went in. Whisk in a little extra warm liquid to loosen it.
Why is my roux-based sauce too thin?
There is not enough roux for the volume of liquid, or the sauce has not been simmered for long enough after the liquid was added, a roux needs a few minutes of gentle cooking to thicken fully.
How much roux do I need to make a gravy or cheese sauce?
Enter the volume of liquid and the thickness you want above for the exact weight of butter and flour. A thin, pouring sauce needs the least roux per 500ml, a thick, binding sauce needs the most.