ABV Calculator

Calculate alcohol by volume from gravity readings (SG or Plato/Brix), with ABW, apparent attenuation, calories, and a priming sugar calculator for bottle conditioning.

Formula: ABV = (OG - FG) × 131.25 Alternative (more accurate at high ABV): ABV = 76.08 × (OG - FG) / (1.775 - OG)
ABW = ABV × 0.7936 / FG  |  Apparent Attenuation = (OG - FG) / (OG - 1) × 100
Tip: Ensure both readings use the same unit (both SG or both Plato). Hydrometers are calibrated at 20°C / 68°F - temperature-correct your readings for accuracy. CO2 in samples lowers the reading; degas before measuring.

Priming Sugar Calculator

Calculate how much sugar to add for bottle conditioning based on beer volume, target CO2 volumes, and beer temperature.

CO2 guide: 1.5-2.0 volumes = low (British ales, stouts); 2.2-2.7 = standard (most ales, lagers); 2.7-3.5 = high (wheat beers, Belgian ales). Colder beer retains more residual CO2, requiring less priming sugar.

Understanding ABV and Gravity Readings

Alcohol by volume (ABV) is the standard measure of how much ethanol a fermented beverage contains. In brewing, it is calculated from the drop in specific gravity between the unfermented wort (Original Gravity, OG) and the finished beer (Final Gravity, FG). The denser the wort, the more sugar is available for yeast to convert into alcohol and CO2.

The Standard Formula

The most widely used homebrew formula is:

ABV = (OG - FG) × 131.25

For example, an OG of 1.050 and FG of 1.012 gives ABV = (1.050 - 1.012) × 131.25 = 4.99%. This formula is accurate up to about 8-9% ABV; above that, a more complex alternative (76.08 × (OG - FG) / (1.775 - OG)) provides better results because the relationship between gravity and alcohol becomes non-linear.

ABW (Alcohol By Weight)

ABW expresses alcohol as a percentage of weight rather than volume. Because ethanol (density 0.789) is lighter than water, ABW is always lower than ABV. The conversion uses the final gravity of the beer: ABW = ABV × 0.7936 / FG. ABW is still used on beer labels in some countries (historically in the US for beer taxation).

Apparent Attenuation

Apparent attenuation measures how much of the wort's extract the yeast consumed: AA = (OG - FG) / (OG - 1) × 100. It is called "apparent" because alcohol lowers the measured gravity - true attenuation is higher. Typical ranges: 65-70% (sweet, full-bodied), 70-78% (balanced), 78-85% (dry, as in Belgian and some American ales).

Calories in Beer

Beer calories come from two sources: alcohol (7 kcal/g) and residual carbohydrates (about 4 kcal/g). This calculator estimates calories per 12 oz serving (355 ml) and per 500 ml, based on the OG, FG, and resulting ABV.

Priming Sugar for Bottle Conditioning

Bottle conditioning produces natural carbonation by adding a small measured dose of sugar (the "priming" charge) to finished beer at bottling time. Residual yeast consumes the sugar, producing a small amount of CO2 that dissolves into the sealed beer. The amount of sugar depends on:

  • Target CO2 volumes: Style-dependent, from ~1.5 (low-carbonation ales) to ~3.5 (hefeweizen, Belgian). Most beers target 2.2-2.7.
  • Beer temperature: Colder beer retains more dissolved CO2 from fermentation, so less priming sugar is needed. Warmer beer has less residual CO2.
  • Beer volume: The total amount of beer being primed.
  • Sugar type: Corn sugar (dextrose) is the standard; table sugar (sucrose) is ~10% more fermentable by mass; DME (dry malt extract) is less consistent and requires ~40% more by mass.

This calculator uses the residual CO2 equation: CO2(residual) = 3.0378 - 0.050066 × T(°C) + 0.00026555 × T², where T is the beer temperature. The required CO2 from priming is the target minus residual, converted to grams of sugar per volume.

Frequently Asked Questions

What is ABV?

ABV stands for Alcohol By Volume. It is the percentage of a liquid's volume that is pure ethanol. For example, a beer with 5% ABV contains 5 milliliters of ethanol per 100 milliliters of beer. ABV is the standard way to measure alcohol content in beer, wine, and spirits worldwide.

How is ABV calculated from gravity readings?

The most common formula is ABV = (OG - FG) × 131.25, where OG is Original Gravity and FG is Final Gravity measured in specific gravity units. An alternative formula, ABV = 76.08 × (OG - FG) / (1.775 - OG), is slightly more accurate at higher alcohol levels. Both formulas require gravity readings in specific gravity, not Plato or Brix.

What is the difference between ABV and ABW?

ABV (Alcohol By Volume) measures ethanol as a percentage of total volume, while ABW (Alcohol By Weight) measures ethanol as a percentage of total weight. Because ethanol is less dense than water, ABW is always lower than ABV. The conversion is ABW = ABV × 0.7936 / FG (using the beer's final specific gravity).

What is apparent attenuation?

Apparent attenuation is the percentage of sugars consumed by yeast during fermentation, calculated from gravity readings: AA = (OG - FG) / (OG - 1) × 100. Most beer yeasts attenuate 65-80%. Lower attenuation gives a fuller body and sweeter finish; higher attenuation gives a drier, thinner beer.

How do I convert Plato/Brix to specific gravity?

For a quick approximation, SG ≈ 1 + Plato ÷ 260. So 12°P is roughly 1 + 12/260 = 1.046. For precise work, use the polynomial: SG = 1 + (Plato / (258.6 - (Plato × 227.1 / 258.2))). This calculator handles Plato/Brix input automatically when you switch the unit toggle.

How much priming sugar should I use for bottle conditioning?

A common starting point is about 4 g of corn sugar per liter of beer (roughly 3/4 cup for a 5-gallon / 19 L batch) for about 2.5 volumes of CO2. Table sugar requires about 10% less by weight. The exact amount depends on beer temperature (colder beer retains more residual CO2), the target CO2 volume (1.5-3.5), and the beer volume. Use the Priming Sugar tab for a precise calculation.

Why does my ABV seem too high or too low?

Check that OG and FG are in the same units (both specific gravity, not mixed with Plato). Ensure readings are temperature-corrected - hydrometers are calibrated at 20°C / 68°F. A reading taken on fermenting beer with dissolved CO2 will read low; degas the sample first. Make sure FG is lower than OG - if not, fermentation may be incomplete or there is a measurement error.