What is a volume of CO2 in beer carbonation?

One volume of CO2 means one litre of carbon dioxide gas (measured at 0 °C and 1 atm) dissolved in one litre of beer. Most ales sit between 2.0 and 2.8 vol; hefeweizens and Belgian witbiers push to 3.5–4.5 vol. Flat beer is around 0.5–0.8 vol and a commercial lager is typically 2.4–2.7 vol.

Why does fermentation temperature affect the calculation?

During fermentation yeast produces CO2, a portion of which dissolves into the beer. Colder beer absorbs and holds more CO2 — the same volume of beer fermented at 10 °C retains significantly more residual CO2 than the same beer fermented at 20 °C. If you ignore this, you will add too much priming sugar and risk over-carbonated or even gushing bottles. The calculator uses the Fix and Fix (1997) polynomial: residual = 3.0378 − 0.050062·T°F + 0.00026555·T°F², which is the industry-standard equation.

What is the difference between dextrose and table sugar for priming?

Dextrose (glucose) is a monosaccharide with a CO2 efficiency of about 0.476 g CO2 per gram. Table sugar (sucrose) is a disaccharide of glucose and fructose with an efficiency of about 0.465 g CO2 per gram — slightly lower by mass. Either works well for bottle conditioning. Dextrose is marginally cleaner-tasting because yeast does not need to break a glycosidic bond first, but most brewers cannot detect a difference in the finished beer.

Can I use dry malt extract (DME) for priming?

Yes. DME gives a lower CO2 yield per gram (about 0.408 g CO2/g) because only roughly 68% of its weight is fermentable simple sugars. You need to add more DME by mass than dextrose, but it adds very slight malt body and is preferred by some extract brewers who want to avoid adding a refined sugar to an all-malt recipe. Make sure to boil the DME solution briefly to sanitise before adding to the bottling bucket.

How do I ensure even carbonation across all bottles?

The safest approach is bulk priming: dissolve the full calculated sugar amount in 250–500 ml of boiling water, let it cool, and gently stir it into your bottling bucket before racking the beer. Racking on top of the priming solution, and stirring once slowly with a sanitised spoon, ensures the sugar is evenly distributed. Avoid splashing to prevent oxidation. Never add a measured amount per bottle unless you are using carbonation drops — uneven distribution leads to bottles with wildly different carbonation levels.

Is it safe to bottle before the beer has fully finished fermenting?

No — this is the single most common cause of bottle bombs. The priming sugar calculation assumes the beer has zero residual fermentable sugars left from the main fermentation. If you bottle early, the yeast will continue converting the remaining fermentables in addition to the priming sugar, producing far more CO2 than the bottle can hold. Always confirm fermentation is complete by taking two hydrometer or refractometer readings 48–72 hours apart. Both readings should be identical before you bottle.

Priming Sugar Calculator

The priming sugar calculator tells you exactly how many grams of fermentable sugar to add to your beer to achieve a precise level of carbonation during bottle conditioning. It accounts for the CO2 already dissolved in your beer — a function of fermentation temperature — so you only add what is actually needed.

How bottle carbonation works

When you seal beer in a bottle with a small amount of fermentable sugar, the residual yeast consumes that sugar in an oxygen-free environment. Because the CO2 produced has nowhere to escape, it dissolves into the beer under pressure. After two to four weeks at room temperature the yeast finishes its work, drops out of suspension, and you are left with naturally carbonated beer.

The art is adding exactly the right amount of sugar. Too little and the beer is flat; too much and you risk over-carbonated gushers or, in extreme cases, bottle explosions.

The formula

Carbonation is measured in volumes of CO2 — the number of litres of gas (at 0 °C, 1 atm) dissolved per litre of beer.

Step 1 — residual CO2. Beer already holds some CO2 from fermentation. The amount depends on the highest temperature the beer reached during active fermentation, modelled by the Fix and Fix polynomial:

residual = 3.0378 − 0.050062 · T°F + 0.00026555 · T°F²

For example, beer fermented at 20 °C (68 °F) retains approximately 0.86 vol before priming.

Step 2 — CO2 to add.

CO2 to add (vol) = target vol − residual vol

Step 3 — mass of CO2 needed. One volume of CO2 equals 1.96 g of gas per litre of beer:

CO2 mass (g) = CO2 to add × beer volume (L) × 1.96

Step 4 — mass of sugar. Each sugar releases a known amount of CO2 when fully fermented:

sugar (g) = CO2 mass (g) ÷ efficiency (g CO2 / g sugar)

Sugar	Efficiency
Dextrose (anhydrous glucose)	0.476 g CO2/g
Corn sugar monohydrate	0.432 g CO2/g
Sucrose (table sugar)	0.465 g CO2/g
Dry malt extract (DME)	0.408 g CO2/g
Honey	0.370 g CO2/g
Brown rice syrup	0.455 g CO2/g
Pure maple syrup	0.280 g CO2/g

Worked example

You have brewed 19 litres of an American IPA. The beer reached a peak fermentation temperature of 20 °C (68 °F). You want to carbonate to 2.4 volumes using dextrose.

Residual CO2: 3.0378 − 0.050062 × 68 + 0.00026555 × 68² = 0.861 vol
CO2 to add: 2.4 − 0.861 = 1.539 vol
CO2 mass: 1.539 × 19 × 1.96 = 57.3 g CO2
Dextrose: 57.3 ÷ 0.4762 = 120.3 g

That is about 3.2 g per 500 ml bottle or 2.1 g per 330 ml bottle.

Typical carbonation targets by style

Style	Target (vol CO2)
British cask ale	1.0–1.5
British bottled ale	1.5–2.2
American IPA	2.2–2.7
American lager	2.4–2.9
German Pilsner	2.4–2.9
Stout / Porter	1.7–2.3
Saison	2.8–3.5
Belgian witbier	2.9–3.3
Hefeweizen	3.6–4.5
Lambic / Gueuze	3.0–4.5

Enter any target in the calculator above, or pick a style preset to load its midpoint automatically. Every calculation runs entirely in your browser — no data is sent to a server.