For a beer sitting at 68°F since fermentation, bottle-conditioning a full 5-gallon (18.9 L) batch to a standard 2.4 volumes of CO2 takes 116.7 g of corn sugar (dextrose) — close to the "3/4 cup" rule of thumb printed on a lot of sugar bags (a rounded cup measure of dextrose lands in roughly the same range), but the calculated figure accounts for the CO2 your beer already has dissolved in it, where the flat rule doesn't. Reproduce this exact result or swap in your own volume, temperature and target.
Why "5 gallons of beer" isn't the whole input
Beer at equilibrium with fermentation already holds dissolved CO2 — at 68°F, this batch already carries roughly 0.86 volumes before a single gram of sugar goes in. The calculator only doses for the difference between what's already there and your target: 2.4 target minus 0.86 residual leaves 1.54 volumes still needed, which is what the 116.7 g figure actually corresponds to. This is also why "the warmest the beer got" matters more than "the temperature it is right now" — CO2 a beer has already released during a warm spell doesn't come back once things cool down, so priming math always uses the highest temperature the beer has been at since fermentation finished, not the current fridge or cellar reading.
The number changes with your actual numbers
- Different sugar type, same batch: the same 5 gallons at the same 2.4-volume target needs roughly 105.0 g of table sugar (sucrose ferments slightly more completely per gram than dextrose) or roughly 158.7 g of dry malt extract (DME is only around 65-70% fermentable extract by weight). See corn sugar, table sugar and DME priming ratios for the full comparison.
- A different style target: a British-style ale conditioned lower, around 1.8 volumes, needs meaningfully less sugar than a hefeweizen pushed to 3.8 volumes for the style's traditionally assertive carbonation — see CO2 volumes by style.
- A warmer or cooler fermentation: the same batch sitting at 75°F instead of 68°F already holds less dissolved CO2 (roughly 0.78 volumes) and needs slightly more sugar to hit the same 2.4 target; one that peaked at only 62°F holds more residual CO2 (roughly 0.95 volumes) and needs slightly less. Guessing the temperature rather than checking it is a common source of an over- or under-carbonated batch that otherwise did everything right.
A smaller batch needs proportionally less, not the same amount
If you're only bottling a gallon rather than a full five, don't eyeball a fifth of this dose — see how much priming sugar for 1 gallon, where the real challenge shifts from the arithmetic to weighing a much smaller quantity accurately. And before dosing anything meaningfully above a 2.4-3.0 volume target, read what happens if I use too much priming sugar — overcarbonation in a standard bottle is a genuine glass-safety issue, not just a foam-over risk.