This priming sugar calculator works out how much dextrose or white sugar to add to a batch of beer at bottling so it carbonates to the level you want. It takes the CO2 already dissolved in the beer (which depends on the warmest temperature the beer reached after fermentation) away from your target, then converts the difference into grams of sugar. As a rule of thumb, about 4g of table sugar per litre adds 1 volume of CO2, and dextrose needs about 10% more.
Worked example
A 23L batch of pale ale that finished fermenting at 20°C already holds about 0.86 volumes of CO2. To reach 2.4 volumes it needs about 142g of white sugar, or about 156g of dextrose (roughly 6.8g per litre).
How to bulk prime
- Dissolve the dextrose in a cup of boiled water and let it cool.
- Pour it into a sanitised bottling bucket and gently rack the beer on top so it mixes without splashing.
- Fill and cap the bottles, then keep them at about 18–22°C for two weeks before chilling.
FAQ
Which temperature should I enter?
The warmest temperature the beer reached after fermentation finished, not the temperature on bottling day if it has been cold crashed. Warmer beer holds less CO2, so it needs more sugar.
Dextrose or white sugar?
Both work. Dextrose ferments cleanly and quickly; you need about 10% more of it by weight than table sugar for the same fizz.
Can I use carbonation drops instead?
Yes. Drops are pre-measured per bottle, so they are easy but less precise than bulk priming.
Is it safe to over-prime?
No. Too much sugar can over-pressurise glass bottles. Make sure fermentation has fully finished (stable hydrometer readings) and stick to the calculated amount.
Gear and guides: dextrose, bottles and capping, home brew supplies, how to brew beer at home. More tools: ABV calculator, spirit dilution calculator.
