Priming Sugar Calculator

Priming sugar is the small amount of fermentable sugar added at bottling to create natural carbonation inside the bottle. The yeast consumes it and produces CO2, which dissolves into the beer under pressure.

The Formula:

Sugar (grams) = (Volume of beer in liters) × (Target CO2 volumes − Residual CO2 volumes) × factor

The factor changes by sugar type. Corn sugar is the reference every other number is quoted against:

These come out of the chemistry rather than off a chart. One volume of CO2 means one litre of gas per litre of beer, which weighs 1.963 grams at 0 °C and one atmosphere. Sucrose ferments four molecules of CO2 to one of sugar, so 342.3 grams of it yields 176.0 grams of gas, and the dose falls out as 3.82 g/L per volume. Dextrose ferments two to one from a heavier molecule, so it takes more.

Table sugar is the lighter dose, which surprises people who assume corn sugar is the purer product. The reason is water. Brewing corn sugar is dextrose monohydrate, and about a tenth of what you weigh out is water of crystallization locked into the crystal, contributing nothing. Sucrose has none, so you need roughly 14% less of it by weight for the same carbonation.

DME is looser. It is only partly fermentable, and how partly depends on the extract, so about 1.4× corn sugar is a planning figure rather than a constant. Brewers who prime with DME usually accept a slightly wider carbonation spread as the price of not adding refined sugar to the beer.

Residual CO2 is the CO2 already dissolved in the beer, and it is set by the warmest temperature the beer reached after fermentation finished. Warm beer holds less. Get this wrong and the error goes straight into the sugar dose.

Worked Example:

• Batch size: 5 gallons (18.9 liters), which is what the calculator above asks for
• Target carbonation: 2.4 volumes (typical American ale)
• Fermentation temp: 68 °F (20 °C) → residual CO2 = 0.87 volumes
• Using table sugar

In the per-gallon form the calculator uses: 0.510 × (2.4 − 0.87) × 5 = 3.90 oz

In grams per liter, which is the same sum: 18.9 × 1.53 × 3.82 = 111 grams

Corn sugar for the same beer comes to 4.51 oz, or 128 grams. That gap is the water in the crystal, not a different target.

Carbonation targets by style

Bottles have a ceiling, and it is lower than people think

Standard brown longneck bottles are rated to roughly 4 volumes at room temperature, and that rating assumes an undamaged bottle. Every trip through a bottle brush and a crate scratches the glass a little. Above about 3.0 volumes, use heavy Belgian bottles or champagne bottles with a cage, and store the crate in a plastic tub or a cardboard box either way. A bottle failing at 4 volumes is not a leak, it is a grenade.

The other half of that risk is fermentation that was not actually finished. Two identical gravity readings three days apart is the only evidence that counts, and it is worth more than any calculator on this page.

Practical Tips:

• Dissolve sugar in about 250 mL of boiled, cooled water before adding to the bottling bucket
• Stir gently. Splashing at this stage oxidizes the beer and there is no fixing it afterwards
• Condition bottles at 18 to 22 °C for at least 2 weeks before chilling. Cold beer stops carbonating
• If you bottle straight from a fermenter that has been cold-crashed, use the warmest temperature the beer saw after fermentation ended, not the cold-crash temperature