Top-down Brew: Priming Sugar Calculator

Purpose: This calculator determines the amount of priming sugar needed to achieve a desired level of carbonation.

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The beginner method of using 3/4 cup of corn sugar (anhydrose glucose or glucose monohydrate) for priming a five gallon batch is simple but it has some serious drawbacks. The present calculator offers a more precise method to determine the needed amount of priming sugar and control the desired level of carbonation. In brief, the calculator works by determining the difference between residual carbonation (the dissolved carbon dioxide at the end of fermenation; from Henry's Law) and the desired level of carbonation in the bottle. This difference is used to calculate the weight of sugar needed to achieve the target level of carbonation. For further details, please refer to McGill (2006) and Smith (2015).

Basic carbonation reference (volumes of CO2):

Using over 3.0 volumes of CO2 is unsafe for standard bottles. Highly carbonated beers need reinforced Belgian ale bottles that have corks held in place with a wire basket.

Most homebrewers use corn sugar for priming, and this usually comes in the anhydrous dextrose form. Table sugar (sucrose) is harder for the yeast to digest because a glucose-fructose bond must be split before the sugar can be consumed by the yeast.

Some residual carbon dioxide may be lost during bottling process, such as the transfer into a bottling bucket and bottle filling. The calculator does not account for carbon dioxide losses during packaging. It may be necessary to slightly overshoot the carbonation goals to compensate for this lost carbon dioxide.

If multiple temperatures were maintained during fermentation, the highest temperature is the one that should be used in the calculator. For example, an lager fermentation might start at 52 degrees F, followed by a diacetyl rest at 65 F for a few days, and then lagering at 40 F when primary fermentation is finished. The proper temperature to use in this situation would be 65 F. In a similar manner, if an ale primary fermentation at 68 degrees F is followed by cold crashing at 40 F, the proper temperature to use is 68 F.

One additional tip is to stir the beer gently in the bottling bucket with a sanitized spoon before filling the bottles. This will ensure that the priming sugar is mixed evenly throughout the beer. Failure to evenly mix the sugar can produce uneven carbonation.


Lewis, A. (2010). Better bottling. Brew Your Own, 16(1), 16-18.

McGill, R. (2006). Priming with sugar. Brew Your Own, 12(7), 44-47.

Palmer, J.J. (2002) How to Brew. 2nd edition, Defenestrative Publishing, p. 133

Smith, B. (2015). Solve the priming puzzle. Brew Your Own, 21(3), 76-80.

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