Priming Sugar Calculator
Enter your beer volume, highest temperature reached, and target CO₂ volumes.
Result
How it is calculated
The temperature (°C) is first converted to °F, T = °C × 9/5 + 32, and the CO₂ still dissolved in the beer is estimated as residual = 3.0378 − 0.050062·T + 0.00026555·T² volumes. The sugar must supply the difference: needed = target − residual (never below zero). Dextrose in grams is needed × 4.0 × volume (litres), and table sugar is dextrose × 0.91, because sucrose yields more CO₂ per gram. Dextrose and table sugar are shown to one decimal in grams, the residual to two decimals in volumes of CO₂. Volume, target and temperature are all required. The polynomial is meant for ordinary fermentation temperatures, so do not trust it for extreme values.
Worked example
20 litres of beer, highest temperature 20 °C, target 2.4 volumes. In Fahrenheit: 20 × 9/5 + 32 = 68. Residual CO₂: 3.0378 − 0.050062 × 68 + 0.00026555 × 68² = 0.86 volumes. Needed: 2.4 − 0.86 = about 1.54 volumes. Dextrose: 1.54 × 4.0 × 20 = 123.1 g. Table sugar: 123.1 × 0.91 = 112.0 g. If the target were only 0.5 volumes (below the residual), the tool would show 0.0 g of both sugars.
Common mistakes
- Entering the temperature at bottling (cold cellar) instead of the highest temperature the beer reached after fermentation; the dissolved CO₂ is set by the warm peak, so a low value adds too much sugar.
- Entering the volume of the whole fermenter instead of the volume of beer actually being bottled, which overstates the sugar.
- Entering a target in g/L or bars rather than volumes of CO₂; typical values are around 2 to 3 volumes.
- Weighing table sugar with the dextrose figure; sucrose needs about 9 % less by weight, and the tool lists both separately.
- Using a priming amount for a different sugar such as honey, malt extract or brown sugar; the tool only covers dextrose and table sugar.
About this calculator
Priming sugar is the measured amount of fermentable sugar — usually corn sugar (dextrose) or table sucrose — added to beer just before bottling so residual yeast can ferment it and produce the CO₂ that carbonates the beer naturally in the sealed bottle. The correct amount depends on the target carbonation level in volumes of CO₂ (typically 2.2–2.8 for most ale styles, higher for Belgian styles), the beer's volume, and critically the highest temperature the beer reached during fermentation, since warmer beer already holds less dissolved residual CO₂ and needs more priming sugar to reach the same final carbonation.
Homebrewers use this calculation on every batch before bottling day, since too little sugar leaves the beer flat while too much can over-carbonate bottles to the point of gushing or, in rare cases, bottle bombs.
This calculator takes your batch volume, the highest temperature the beer reached, and your target CO₂ volumes, then returns the precise amount of corn sugar or table sugar to add for safe, accurate carbonation.
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