Priming Sugar Calculator

Background.

Beer coming out of the fermenter is not flat. Fermentation leaves it saturated with its own carbon dioxide, and how much stays dissolved depends on temperature: at 20 °C a beer still carries about 0.86 volumes of CO2, more than a third of a 2.4-volume target in the middle of Brew Your Own's range for American ales. Priming sugar only has to make up the difference, and forgetting what is already there is a common route to gushing bottles.

Carbonation is counted in volumes: the space the dissolved CO2 would take up as a gas at 0 °C and one atmosphere, divided by the volume of beer. The brewing industry takes one volume in a litre of beer as 1.96 g of CO2. Yeast turns sugar into CO2 and ethanol in fixed proportions, so the grams of gas still needed translate directly into grams of sugar: 128.997 g of corn sugar for 19 litres going from 0.86 to 2.4 volumes.

The kind of sugar changes that mass. The dextrose monohydrate sold as corn sugar or priming sugar yields 0.4442 g of CO2 per gram, against 0.5143 for table sugar, because about 9 percent of its weight is water locked into the crystal. Recipes that say just "dextrose" seldom say whether they mean this form or the anhydrous one, and the two differ by 10 percent.

The calculator also gives the pressure inside the bottles once the CO2 has dissolved, and that depends on where they are kept. A 2.4-volume ale stored at 20 °C sits at about 26.2 psi above atmospheric; in a 4 °C fridge it relaxes to 9.1 psi; in a 30 °C room it rises to 35.9 psi. Real bottles run a little higher, since air trapped at capping is ignored.

What is priming sugar calculator?

Priming sugar is the measured dose of fermentable sugar stirred into finished beer at bottling, so that the yeast still in suspension carbonates it inside the sealed bottle, a process called bottle conditioning. The dose depends on three things: the CO2 the beer already holds, the carbonation wanted, and how much CO2 each gram of the chosen sugar releases. Run the other way, the same arithmetic shows what carbonation a recipe's stated sugar amount will give.

How to use this calculator.

1. 01Choose the direction: sugar for a target carbonation on bottling day, or the carbonation a given amount of sugar will give.
2. 02Enter the litres of beer actually going into bottles, after the sediment is left behind. Five US gallons is 18.93 L.
3. 03Set the target in volumes of CO2. Brew Your Own's chart gives British ales 1.5–2.2, American ales 2.2–3.0, European lagers 2.4–2.6, American lagers 2.5–2.8, Belgian ales 2.0–4.5 and German weizens 2.8–5.1.
4. 04Enter the warmest temperature the beer reached after fermentation finished, not today's temperature: warming drives CO2 out and cooling does not put it back.
5. 05Enter the temperature the bottles will condition and be stored at; it changes the pressure, not the sugar.
6. 06Pick the sugar. For dry malt extract, honey or anything else that is not a pure sugar, choose the last option and enter its fermentable sugar percentage.

The formula.

The CO2 already dissolved comes from Michael Hall's correlation, published in Zymurgy in 1995: V_residual = 3.0378 − 0.050062·T + 0.00026555·T², with T the beer temperature in °F. The sugar is then (V_target − V_residual) × 1.96 × litres ÷ Y, where Y is grams of CO2 per gram of sugar. The yields come from the fermentation equations, glucose → 2 ethanol + 2 CO2 and sucrose + water → 4 ethanol + 4 CO2, with IUPAC 2021 molar masses: 4 × 44.009 ÷ 342.297 = 0.5143 for sucrose, 2 × 44.009 ÷ 180.156 = 0.4886 for anhydrous glucose and 2 × 44.009 ÷ 198.171 = 0.4442 for the monohydrate. A custom fermentable is treated as glucose at the percentage you enter. Bottle pressure uses Henry's law: since Hall's figure is what the beer holds under one atmosphere of CO2, holding V_final needs V_final ÷ V_residual(storage) atmospheres absolute, less one for gauge. The 1.96 g/L convention sits between the ideal-gas density of CO2 at 0 °C, 1.9635 g/L, and the measured 1.977 g/L. Temperatures are limited to −2 to 30 °C because Hall's parabola bottoms out at 94.26 °F (34.59 °C) and above that would wrongly predict warm beer holding more gas.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Hall, Michael L. "Brew by the Numbers: Add Up What's in Your Beer." Zymurgy 18(2), Summer 1995, American Homebrewers Association — the source of the residual-CO2 correlation CO2(volumes) = 3.0378 − 0.050062·T + 0.00026555·T², with T in °F, which almost every homebrew carbonation calculator in use today is built on. Print / archived; not available as an open web document.
2. [2]Brew Your Own magazine, "Carbonation Priming Chart" — Section A, carbonation levels by style (British ales 1.5–2.2, American ales 2.2–3.0, European lagers 2.4–2.6, American lagers 2.5–2.8, Belgian ales 2.0–4.5, German weizens 2.8–5.1); Section B, residual CO2 by temperature; Section C, volumes of CO2 produced by anhydrous glucose, glucose monohydrate and sucrose in 5 gallons. The three band edges used on this page (1.5, 3.0 and 4.5 volumes) are the extremes of Section A.
3. [3]Smith, Brad. "Calculating Sugar Additions for Carbonation." Brew Your Own — states the volumes-of-CO2 convention and the conversion "one volume is 1.926 grams/liter of CO2", and gives the widely used corn-sugar constant Weight_grams = 4.01 × Vol_liters × (Vols_desired − residual). That 4.01 figure is 1.96 g/L divided by the CO2 yield of anhydrous dextrose, which is how the 1.96 g/L convention on this page is pinned — and a reminder that the constant assumes the anhydrous form, not the monohydrate homebrew shops sell.
4. [4]IUPAC Commission on Isotopic Abundances and Atomic Weights, Standard Atomic Weights 2021 — C 12.011, H 1.008, O 15.999, giving CO2 44.009, sucrose 342.297, glucose 180.156, glucose monohydrate 198.171 and ethanol 46.069 g/mol. These molar masses fix the CO2 yield of every pure priming sugar on this page.
5. [5]Thompson, A. and Taylor, B.N. NIST Special Publication 811, "Guide for the Use of the International System of Units (SI)", 2008 edition — the exact conversions used here: 1 avoirdupois ounce = 28.349523125 g, 1 standard atmosphere = 101 325 Pa, 1 psi = 6 894.757293168 Pa, 1 bar = 100 000 Pa. Ethanol density 0.78934 g/mL at 20 °C is the standard tabulated value used for the ABV that priming adds.