Priming Sugar Calculator
The beer already holds CO2 from fermentation — ignoring it is how bottles burst.
The formula
sugar = (target volumes - residual CO2) * 4 g per litre per volume
The beer already holds CO2
Fermentation leaves dissolved carbon dioxide in solution, and how much depends on the temperature the beer has been sitting at — cold beer holds more. Priming sugar only has to make up the difference to the target, so ignoring the residual over-carbonates, sometimes enough to burst bottles.
Volumes of CO2
One volume means the dissolved gas would occupy the same space as the beer at standard conditions. British ales sit around 1.5 to 2.0, American ales 2.2 to 2.7, wheat beers and Belgians 3.0 and above. Above about 3.5 the pressure exceeds what ordinary crown-capped bottles are designed for.
Weigh it, and boil it
Corn sugar and table sugar differ in fermentable content by about 10 %, so a volume measure of one is not a substitute for the other. Dissolving the sugar in boiled water and mixing it gently through the whole batch matters as much as the quantity: uneven priming gives you flat bottles and gushers from the same fermenter.
Recipes are starting points
Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.