Priming Sugar Calculator

Background.

Bottle conditioning is a second, tiny fermentation. You add a measured amount of sugar to finished beer, cap it, and the yeast still in suspension turns that sugar into carbon dioxide with nowhere to go. Get the amount right and the beer pours with the head the style wants. Get it wrong in one direction and it is flat; get it wrong in the other and the bottle becomes a pressure vessel it was never designed to be. This calculator sizes the addition, and it also tells you the pressure the glass will be holding, which is the number most priming calculators leave out.

Carbonation is measured in volumes of CO2 — the volume the dissolved gas would occupy as a gas at 0 °C and one atmosphere, divided by the volume of the beer. The brewing industry's conversion is that one volume equals 1.96 grams of CO2 per litre, and that figure is used here as a definition. It sits between the ideal-gas density of carbon dioxide at those conditions, 1.9635 g/L, and the real-gas density, 1.977 g/L; over a 19 litre batch the difference between the three is under a gram of sugar, which is why the industry rounds and why this page says so rather than presenting 1.96 as a measurement.

Two things then decide the answer. The first is that your beer is not starting from zero. Beer that has just finished fermenting is saturated with its own CO2 at roughly one atmosphere, and how much it holds depends on temperature — cold beer holds a lot, warm beer holds much less. The relevant temperature is the warmest the beer reached after fermentation finished, because warming drives CO2 out and cooling it again does not bring it back. At 20 °C a beer already carries 0.86 volumes, more than a third of a typical 2.4 volume target, and ignoring that is the most common way homebrewers over-prime. This page uses Michael Hall's published correlation for that residual, the one almost every homebrew carbonation calculator is built on, and it names the temperature range over which the correlation behaves.

The second is stoichiometry, and it is exact. Yeast splits sugar into ethanol and carbon dioxide in fixed proportions, so every gram of CO2 in the bottle traces back to a known mass of sugar. Sucrose yields 0.514 grams of CO2 per gram, anhydrous dextrose 0.489, and dextrose monohydrate — which is what homebrew shops actually sell as corn sugar or priming sugar — only 0.444, because nine percent of its mass is water of crystallisation that does not ferment. That 10 percent gap between the two dextroses is a real source of confusion: published priming constants frequently do not say which one they mean. This calculator shows the yield it used as an output so you can check it against your own packet.

The result comes with the pressure. Because the residual-CO2 correlation is the solubility at one atmosphere, Henry's law turns any carbonation level and any storage temperature straight into a bottle pressure. A 2.4 volume ale sitting at 20 °C is holding about 26 psi of gauge pressure; the same beer at 4 °C is holding about 9. That is why bottles that survive a cold cellar burst in a warm car, and it is why the storage temperature is a field on this page rather than an assumption.

What is priming sugar calculator?

Priming sugar is the measured dose of fermentable sugar added to finished beer, cider or mead just before bottling, so that the yeast remaining in suspension carbonates it inside the sealed bottle. The technique is called bottle conditioning, and it is how beer was carbonated for centuries before forced carbonation with a CO2 cylinder existed.

A priming sugar calculator answers the sizing question. It takes the volume of beer, the carbonation you want in volumes of CO2, the warmest temperature the beer reached after fermentation, and which sugar you are using, and returns a mass. Internally it does three things: works out how much CO2 the beer is already carrying, subtracts that from the target to get the CO2 the sugar must supply, and divides by the CO2 yield of that particular sugar.

This page also runs the calculation backwards — you give it a sugar amount and it tells you what carbonation and what bottle pressure that produces — and it reports the small amount of alcohol the priming ferment adds, which falls out of the same balanced equation as the CO2.

How to use this calculator.

1. 01Choose the direction. Bottling day is "sugar needed for a target carbonation"; checking a recipe or a packet you already own is the other one.
2. 02Enter the volume of beer that will actually go into bottles, in litres. Five US gallons is 18.93 L. Leave the trub behind — it is not beer.
3. 03Set the target carbonation. If you do not know it for your style, the chart in the hint under that field covers the common families: 1.5–2.2 volumes for British ales, 2.2–3.0 for American ales, 2.4–2.6 for European lagers, up to 5.1 for German weizens.
4. 04Enter the warmest temperature the beer reached after fermentation finished. This is the field people get wrong, and it is worth being honest about — if the beer sat at 22 °C for a week before you got round to bottling, that is the number, not the 18 °C you fermented at.
5. 05Enter where the bottles will sit while they condition. It does not change the sugar, only the pressure, so use the warmest place they will realistically live.
6. 06Pick your sugar. If it is dry malt extract, honey or anything else that is not a pure sugar, choose "something else" and enter its fermentable sugar percentage yourself.
7. 07Read the sugar mass, then read the pressure figure beside it. Dissolve the sugar in boiled water, cool it, and stir it into a bottling bucket rather than dosing bottles individually or dumping it into the fermenter.

The formula.

The residual CO2 comes from Michael Hall's correlation, published in Zymurgy in Summer 1995 and used by essentially every homebrew carbonation calculator since: CO2 in volumes equals 3.0378 minus 0.050062 times the temperature in Fahrenheit plus 0.00026555 times that temperature squared. Celsius input is converted before it is applied. At 20 °C, which is 68 °F, it gives 0.8614872 volumes.

That correlation is a quadratic fit, and it is worth knowing where it stops behaving. Its parabola bottoms out at 94.26 °F, or 34.59 °C, and rises after that, which is physically wrong — CO2 solubility falls monotonically with temperature. The temperature fields are therefore capped at 30 °C, below the turning point. Over the range that matters for beer the fit is good: it gives 1.7077 volumes at 0 °C and 0.8615 at 20 °C, against published carbon dioxide absorption coefficients in water of 1.713 and 0.878 at those temperatures, agreeing to within about two percent.

The sugar mass then follows directly. The CO2 the sugar must supply is the target minus the residual, converted to grams by multiplying by 1.96 g per litre per volume and by the litres of beer, and divided by the CO2 yield of that sugar. The yields are stoichiometric, not empirical: fermentation of glucose gives two molecules of CO2 per molecule of sugar, and sucrose hydrolyses first and gives four, so with IUPAC 2021 atomic weights sucrose yields 4 × 44.009 / 342.297 = 0.5142785 g of CO2 per gram, anhydrous dextrose 2 × 44.009 / 180.156 = 0.4885655, and dextrose monohydrate 2 × 44.009 / 198.171 = 0.4441518.

The worked example runs 19 litres of ale, last held at 20 °C, up to 2.4 volumes with corn sugar. The beer already carries 0.86 volumes, so the sugar has to supply 1.54, which is 57.29 g of CO2, which is 128.997 g of dextrose monohydrate — 4.55 oz, or 6.79 g per litre. Change nothing but the sugar and the mass changes with the yield: 111.41 g of table sugar, 117.27 g of anhydrous dextrose, or 146.59 g of a fermentable that is 80 percent sugar. All four make exactly the same 57.29 g of CO2.

Bottle pressure uses Henry's law, which is linear in partial pressure. Because the residual correlation is the amount of CO2 the beer holds at one atmosphere, the absolute CO2 pressure needed to hold the final carbonation in solution at the storage temperature is simply the final volumes divided by the residual at that temperature. At 2.4 volumes and 20 °C storage that is 2.4 / 0.8614872 = 2.786 atmospheres absolute, so 1.786 atmospheres of gauge pressure: 26.25 psi, or 1.81 bar. Store the same bottles at 4 °C and the gauge pressure falls to 9.08 psi. The model assumes a pure-CO2 headspace at equilibrium and ignores air trapped when the cap went on, which makes it a slight under-estimate.

The alcohol comes out of the same balanced equation. Each gram of CO2 arrives with 46.069 / 44.009 = 1.0468 grams of ethanol, so the example's 57.29 g of CO2 comes with 59.98 g of ethanol; at an ethanol density of 0.78934 g/mL and 19 litres of beer that is 0.40 percentage points of ABV.

Nothing is rounded at an intermediate step. Every quantity is carried at forty significant digits and rounded once, at the end, to ten decimal places. The band is decided from the unrounded final carbonation, and it deliberately does not restate the number, so it cannot contradict the two-decimal figure displayed beside it.

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.