Basics and units

Priming sugar (sucrose)

6 or 8 g per litre? It depends on the temperature of your beer, and it is the difference between a flat beer and a gusher.

Result

Fill in the values and run the calculation, or try the example.

This is the calculation Krausi uses. Create an account to save it in a recipe or a brew.

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Why calculate the priming sugar?

Priming is the step most often done by eye, and the least forgiving one. Too little sugar gives a flat beer. Too much gives bottles that gush when opened, and in the worst case bottles that explode.

What many people do not know: beer already contains CO2 at the end of fermentation, and the colder it stayed, the more it holds. A lager fermented at 12 °C retains 1.12 volumes, an ale fermented at 20 °C only 0.86. The sugar dose must top up the gas already there, not replace it.

You do this calculation on bottling day, once the final gravity has been stable for two days.

How is the sugar dose calculated?

The tool first estimates the residual CO2 from the beer temperature, converted to °F, then calculates the missing sugar:

residual CO2 = 3.0378 − 0.050062 × °F + 0.00026555 × °F²
sugar (g/L)  = (target volumes − residual CO2) × 3.92

It takes 3.92 g of sucrose (table sugar) per litre to produce one volume of CO2. The result has been checked to within 0.1 g/L against the 841 cells of a reference table.

The temperature to enter is the highest the beer reached after fermentation ended, not the temperature on bottling day: CO2 that escaped while warm does not come back.

Worked example

Values entered

Target carbonation in volumes of CO2: 2.5
Highest temperature reached by the beer at the end of fermentation, in °C: 20

Result from the tool

Sucrose to add, in g/L (0 if the residual CO2 is enough): 6.42 L
CO2 still dissolved in the beer, in volumes: 0.86 vol.
Note: Dose of sucrose (table sugar) per litre only: for dextrose, honey, extract or a total quantity, use the priming-by-sugar calculator.

What the tool does not do

The result is a dose of sucrose per litre. For dextrose, honey or malt extract, and for the total quantity to weigh, use priming by sugar type.
From 1.5 to 4.3 volumes of CO2 and from 2 to 30 °C.
The calculation assumes fermentation is finished: priming a beer that is still fermenting leads to overpressure.

Frequently asked questions

How much sugar for 20 litres of beer?

For 2.5 volumes of CO2 and a beer kept at 20 °C, allow 6.4 g per litre, about 128 g of table sugar for 20 L.

Which temperature should I enter?

The highest temperature the beer reached after fermentation ended. If it finished at 20 °C then spent a week in the cold, enter 20 °C.

Why do my bottles explode?

Three possible causes: fermentation was not finished at bottling, the sugar dose was too high, or an infection is consuming the remaining sugars. Check that the gravity is stable over two days before bottling, and weigh the sugar.

And with the assistant?

Ask Krausi the same question in plain language: he picks this tool, does the calculation and files the result in your project.

I'm bottling tomorrow, 20 L, beer at 20 °C. How much sugar for 2.5 volumes?

You need 6.4 g of sugar per litre, so 128 g for your 20 L. Dissolve it in a little boiled water before mixing it into the beer. I've noted the dose in the brew.

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