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Priming Sugar Calculator (Bottle Carbonation)

Calculate exact grams of priming sugar for your target CO₂ volume by style (ale, lager, hefe, saison), batch size and final fermentation temperature.

Built and maintained by Paul Clark, Redmoon Software · Checked against what this tool computes on

Priming sugar needed
0 g
0 oz · Residual CO₂ — vols · Needs — vols
Sugar typeGramsOunces
Quick reference

Residual CO₂: 3.0378 − (0.050062 × T_F) + (0.00026555 × T_F²) — beer at room temperature already holds some CO₂ from fermentation.

Needed CO₂: target_vol − residual.

Grams of corn sugar per liter: needed_co2 × 4.0. Other sugars multiply the corn-sugar weight by a factor derived from how much fermentable sugar each actually contains: corn 1.00, sucrose 0.91, DME 1.47, honey 1.11, maple 1.38.

Kegging needs about half the sugar of bottling because the keg headspace is purged with CO₂ at serving pressure.

How it works

Bottle carbonation is a two-step calculation and the tool shows both steps. First it estimates the CO₂ already dissolved in the beer from temperature, using the standard curve fit residual = 3.0378 − (0.050062 × T°F) + (0.00026555 × T°F²). At 68 °F that is about 0.86 volumes. It then subtracts residual from your target to get the volumes still needed, and converts using 4.0 grams of corn sugar per litre per volume of CO₂, before applying the sugar factor.

Temperature is the input people get wrong, and it swings the answer hard: the same 2.4 volume target needs far more sugar for beer that sat at 75 °F than at 60 °F. Style presets set the target for you — British Ale 1.8, American Ale 2.4, Lager 2.5, Wheat/Hefe 3.4, Belgian 3.5, Stout/Porter 1.7 — or pick Custom. Sugar type rescales the corn-sugar weight: sucrose 0.91, honey 0.93, maple 1.14, DME 1.47. Kegging halves the total.

The residual-CO₂ curve is an empirical fit, not physics, and it misbehaves at the top of the accepted 32 to 100 °F range: the parabola turns upward past roughly 94 °F, so residual starts climbing again instead of falling. The 4.0 grams per litre constant is likewise a linear approximation. Nothing here checks whether your bottles can survive the pressure, and the keg multiplier of 0.5 is a rule of thumb rather than a derived figure.

Frequently asked questions

Which temperature do I enter, fermentation or bottling temperature?

Enter the highest temperature the beer reached after fermentation finished, before you package it. That peak is what set how much CO₂ stayed dissolved. Entering a cold crash temperature makes the tool think residual CO₂ is high and under-doses your priming sugar.

How much table sugar do I use instead of corn sugar?

Select Table sugar / sucrose and the tool multiplies the corn-sugar weight by 0.91, because sucrose is slightly more fermentable by weight. The comparison table under the result shows all five sugars at once, so you can swap without re-running anything.

Why is there a keg option on a bottling calculator?

For naturally carbonating a keg rather than force carbonating it. Choosing Keg multiplies the sugar by 0.5, since the sealed headspace holds pressure that bottles vent away. If you are force carbonating from a CO₂ tank you do not need priming sugar at all.

How many volumes of CO₂ does a hefeweizen need?

The Wheat / Hefe preset targets 3.4 volumes, the highest style option except Belgian at 3.5. That is a lot of pressure, so use heavy Belgian or champagne bottles rather than standard crown-cap longnecks when you prime to that level.

Can I prime with honey or maple syrup?

Yes, both are listed. Honey carries a 0.93 factor and maple syrup 1.14, so you need slightly less honey and noticeably more maple than corn sugar for the same carbonation. Both also add their own flavour, which corn sugar does not.

Peak temperature, not current temperature

The amount of priming sugar depends on how much CO2 is already dissolved in the beer, and that is determined by the HIGHEST temperature the beer reached after fermentation finished — not by its temperature now.

This is the detail that causes over-carbonation. A beer fermented warm and then chilled retains the lower CO2 content of the warm phase, so priming from the cold temperature adds sugar for CO2 that is not there to begin with.

Why this is the calculation to get right

The failure mode is not a disappointing beer. Over-primed bottles build pressure beyond what the glass is rated for, and bottles do burst — which is why the range of target volumes matters (around 1.8 for a British ale, 2.4 for many lagers, higher for wheat beers and Belgian styles) and why the top of the range should only be used in bottles rated for it.

Sugar type matters too: corn sugar, table sugar and dried malt extract have different fermentable yields per gram, so substituting by weight without adjusting changes the result.

Any residual unfermented sugar or an unfinished fermentation adds to the pressure unpredictably. Confirm stable gravity readings over several days before bottling.

Where these numbers come from

The standard or formula behind this tool, so you can check it rather than take it on trust.

  • Residual CO2 is a function of the highest temperature the beer reached after fermentation, not its current temperature.

    This is the detail that causes over-carbonation, and the failure mode is broken glass rather than disappointing beer. Enter the peak post-fermentation temperature.

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