Calculator
Priming sugar calculator
How much sugar do I add at bottling?
Bottle conditioning carbonates beer by giving the remaining yeast a small, measured amount of fresh sugar to ferment in a sealed container. The carbon dioxide has nowhere to go, so it dissolves into the beer. How much sugar you add determines the final carbonation.
The temperature of the beer matters as much as the sugar, and this is the part most often missed: warm beer has already lost more of the carbon dioxide it held after fermentation, so it needs more priming sugar to reach the same level. Getting this wrong in the other direction is the one genuine hazard in home brewing — too much sugar in a sealed glass bottle produces enough pressure to break it.
Result
- Priming sugar123.1 g
- Table sugar instead112 g
- Residual CO₂ already present0.9 vol CO₂
- CO₂ still needed1.5 vol CO₂
Working
Dextrose (g) = (target volumes − residual volumes) × litres × 4
| Step | Expression | Value |
|---|---|---|
| Residual CO₂ at temperature | polynomial in °F | 0.86 volumes |
| Additional CO₂ required | 2.4 − 0.86 | 1.54 volumes |
| Dextrose | 1.54 × 20 × 4 | 123.1 g |
| As table sugar | dextrose × 0.91 | 112 g |
What it means
Typical targets: 1.5–2.0 volumes for British cask-style ales, 2.2–2.6 for most lagers and pale ales, 3.0 and above for Belgian styles and wheat beer.
Worked example
The example above starts from these values. It is rendered on the server, so the formula, assumptions and limitations are all present whether or not you change anything.
- Result123.1 g
- Table sugar instead112 g
- Residual CO₂ already present0.9 vol CO₂
- CO₂ still needed1.5 vol CO₂
Inputs
| Batch volume | 20 L |
|---|---|
| Target carbonation | 2.4 vol CO₂ |
| Beer temperature | 20°C |
How it is calculated
Dextrose (g) = (target volumes − residual volumes) × litres × 4
What each term means
| residual | CO₂ already dissolved in the beer, which depends on its temperature |
|---|---|
| 4 | Approximate grams of dextrose per litre needed to add one volume of CO₂ |
Step by step
| Step | Expression | Value |
|---|---|---|
| Residual CO₂ at temperature | polynomial in °F | 0.86 volumes |
| Additional CO₂ required | 2.4 − 0.86 | 1.54 volumes |
| Dextrose | 1.54 × 20 × 4 | 123.1 g |
| As table sugar | dextrose × 0.91 | 112 g |
What this assumes
- Fermentation is fully complete. This is not optional — priming a beer that has not finished is the main route to genuinely dangerous bottle pressure.
- Residual CO₂ is taken from the highest temperature the beer reached after fermentation, not its current temperature.
- Healthy yeast remains in suspension to ferment the priming sugar.
Where it stops being reliable
- The residual CO₂ figure is an approximation, and using the wrong temperature is the most common source of error.
- Bottles have a pressure limit. Target carbonation above roughly 3 volumes needs bottles rated for it — standard crown-capped bottles are not.
What the number means
Typical targets: 1.5–2.0 volumes for British cask-style ales, 2.2–2.6 for most lagers and pale ales, 3.0 and above for Belgian styles and wheat beer.
Industry convention. A figure brewers have agreed on rather than one derived from first principles. Widely consistent, and worth knowing it is a convention.
Sources: The temperature dependence is Henry’s law: CO₂ solubility in beer falls as temperature rises (Heliyon 9(11):e21493, 2023).
Not traced to a source: The polynomial giving residual volumes from °F. The four grams of dextrose per litre per volume of CO₂.