Beer priming sugar calculator
How much priming sugar to add at bottling for your target CO₂ volumes and batch size — with a worked example and a reference table.
Bottle conditioning is how home brew gets its fizz: you add a small, measured dose of sugar at bottling, the leftover yeast eats it, and the CO₂ they produce is trapped in the sealed bottle. Too little sugar and the beer is flat; too much and you risk gushers — or, at the extreme, bottle bombs. So this isn't a step to eyeball. The good news: the math is simple, and it hinges on two numbers — how carbonated you want the beer (in "volumes" of CO₂) and how much beer you're bottling.
What "volumes of CO₂" means
One "volume" of CO₂ is one liter of dissolved CO₂ per liter of beer. Different styles want different levels:
- British ales: ~1.5–2.2 volumes (gentle)
- American ales, porters, stouts: ~2.2–2.7 volumes (standard)
- Wheat beers, Belgians, saisons: ~2.7–4.5 volumes (lively to high)
Most first batches land happily around 2.4–2.5 volumes — a clean, pub-style fizz.
The dosing rule (corn sugar)
Corn sugar (dextrose) is the standard reference priming sugar. The widely used figure — matching Palmer's tables — is about 4 grams of corn sugar per liter of beer, per volume of CO₂ you want to add. (More precisely ~3.9–4.2 g/L; we'll use 4.0 g/L for clean arithmetic.) The catch is the words "to add": your beer already holds some residual CO₂ left over from fermentation — roughly 0.8–1.0 volumes for a beer fermented at typical ale temperatures. So you only prime for the gap between your target and what's already in there.
The formula:
grams of corn sugar = 4.0 × (target volumes − residual volumes) × liters of beer
Table sugar (sucrose) is a touch more potent — use about 91% of the corn-sugar weight. Dry malt extract (DME) is weaker — use about 1.5× the corn-sugar weight.
Worked example: 5 gallons to 2.5 volumes
Say you've fermented a 5-gallon (≈18.9 L) American pale ale at 68°F and you want 2.5 volumes of CO₂.
- Residual CO₂ at ~68°F ≈ 0.9 volumes
- Volumes to add = 2.5 − 0.9 = 1.6 volumes
- Corn sugar = 4.0 × 1.6 × 18.9 = ≈ 121 grams (about 4.3 oz, a bit over ½ cup)
If you only had table sugar: 121 × 0.91 ≈ 110 g. With DME: 121 × 1.5 ≈ 182 g. Dissolve the sugar in ~1–2 cups of boiling water, cool it, and gently mix it into the bottling bucket before you rack the beer in — even distribution is what keeps every bottle equally carbonated.
Quick reference: corn sugar for a 5-gallon batch
Assuming ~0.9 residual volumes (ale fermented near 68°F) and 18.9 L of beer:
| Target CO₂ (volumes) | Style feel | Corn sugar |
|---|---|---|
| 2.0 | British ale | ~83 g (2.9 oz) |
| 2.2 | Mild / porter | ~98 g (3.5 oz) |
| 2.4 | Standard ale | ~113 g (4.0 oz) |
| 2.6 | American ale | ~129 g (4.5 oz) |
| 3.0 | Wheat / Belgian | ~159 g (5.6 oz) |
Scale linearly for other batch sizes (for a 2.5-gallon batch, halve the numbers). And weigh the sugar — a kitchen scale beats the "5 oz per batch" folk wisdom, which ignores both your target and your residual CO₂.
First, confirm fermentation is finished before bottling — take a stable hydrometer reading on two consecutive days. Priming on top of unfinished fermentation is how you get bottle bombs. Second, measure the sugar by weight, not by eye; "a scoop" is exactly how over-carbonation happens. Then give bottles ~2 weeks at room temperature to condition before you chill and taste.
Gear this guide uses
To prime accurately you need the sugar, a scale, and a way to confirm fermentation is done.
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- Corn sugar (dextrose) priming sugar — the reference priming sugar this math is built on.
- A small digital gram scale — weigh the dose; don't eyeball it.
- A hydrometer and test jar — confirm fermentation is finished before you bottle.
Sources
General guidance, not a substitute for your own readings. Residual CO₂ depends on your fermentation temperature, so treat these as close estimates and round conservatively. Bottle conditioning relies on live yeast and sealed bottles — and as with every step, sanitation is the #1 beginner failure: sanitize bottles, caps, and the bottling bucket before filling.