How this ABV calculator works
Yeast turns sugar into alcohol and carbon dioxide. Sugar makes liquid denser and alcohol makes it lighter, so the drop in density between your first and last readings tells you how much alcohol was made. This page turns those readings into alcohol by volume (ABV), and for mixed drinks it simply adds up the alcohol in each ingredient.
Beer: the standard and alternate formulas
Most homebrew software uses this simple formula [1][2]:
ABV = (OG − FG) × 131.25
It works well for typical beers. For strong beers, wines and meads it tends to read low, so we also show a more detailed formula that accounts for the gravity of the starting wort [1][2]:
ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)
When the simple formula gives more than about 8% ABV, the calculator shows the alternate result as the main number. Both are estimates. The two can differ by close to a percentage point at high gravity: Brewer’s Friend’s example of OG 1.092 and FG 1.021 gives 9.32% by the simple formula and 10.17% by the alternate one [1].
Attenuation, alcohol by weight and calories
- Apparent attenuation is the share of the original gravity points the yeast used up: 100 × (OG − FG) / (OG − 1). A beer going from 1.050 to 1.010 is 80% attenuated [3]. It’s “apparent” because alcohol makes the final reading lower than the sugar left alone would.
- Alcohol by weight (ABW) is about 0.79 × ABV ÷ FG, because alcohol weighs about 0.79 g per mL[2][5].
- Calories use the brewing-chemistry method: 6.9 kcal per gram of alcohol plus 4 kcal per gram of remaining extract (less a small allowance for minerals), scaled to a 12 oz serving[4][2][5]. Real extract is estimated from your OG and FG in °Plato as 0.1808 × OE + 0.8192 × AE. Treat the figure as a ballpark, not a nutrition label.
Specific gravity, Plato and Brix
If your hydrometer reads in °Plato or °Brix, choose that scale and the calculator converts to specific gravity first, using SG = 1 + P / (258.6 − (P / 258.2 × 227.1)) [6]. For homebrewing, Brix and Plato are close enough to treat as the same [6][7]. You can also type gravity as points, like “1050” for 1.050.
Hydrometer temperature correction
A hydrometer is accurate only at the temperature it was calibrated for, usually 59–60 °F (15 °C) on older instruments and 68 °F (20 °C) on newer ones [10][9]. Warm samples are less dense and read low; cold ones read high. The correction scales your reading by the change in water density between the two temperatures [8][9]:
corrected = reading × f(sample °F) / f(calibration °F) f(T) = 1.00130346 − 0.000134722124·T + 0.00000204052596·T² − 0.00000000232820948·T³
For example, 1.050 read at 77 °F on a 68 °F hydrometer corrects to about 1.051 [8]. Corrections get less reliable the further you are from the calibration temperature, so cool hot samples before reading if you can.
Refractometer readings after fermentation starts
A refractometer measures how much light bends in the sample. That works for sugar alone, but alcohol bends light too, so a raw reading taken mid-fermentation or at the end is wrong. Wort isn’t pure sugar either, so readings are first divided by a wort correction factor, usually 1.04, and typically between 1.02 and 1.06[12][13].
The calculator then estimates the real gravity with Sean Terrill’s cubic fit [11][13]:
FG = 1 − 0.0044993·OB + 0.011774·FB + 0.00027581·OB² − 0.0012717·FB² − 0.0000072800·OB³ + 0.000063293·FB³
OB and FB are your original and current Brix readings after dividing by the correction factor. Terrill fitted this to beers that reached at least about 61% apparent attenuation, so results for very sweet or still-fermenting beers, and for wine or mead, are rougher [11][12]. If accuracy matters, check the final gravity with a hydrometer.
Wine, mead and cider
The same hydrometer formulas apply. Dry wines and ciders often finish below 1.000, which is normal because alcohol is lighter than water. The same is why apparent attenuation can come out above 100% for a dry wine. If you add sugar or honey after fermentation to sweeten, use the gravity reading frombefore sweetening as your final gravity, because the added sugar raises the reading without adding alcohol.
Cocktails and mixed drinks
The drink’s ABV is the total pure alcohol divided by the total volume. Each ingredient contributes volume × its ABV. Juice, syrup and mixers add volume but no alcohol. Ice adds water as it melts, which lowers the strength further.
How much water ice adds depends on the ice, how long you stir or shake, and the drink itself, so there is no single right number. The presets come from Dave Arnold’s measurements: about 50% added water for a stirred Manhattan and about 63% for a shaken whiskey sour, as a share of the undiluted drink [14]. For a drink built over ice in the glass, dilution keeps rising as the ice melts, so enter your own figure.
The standard-drink figure uses the US definition of 0.6 fl oz (14 g) of pure alcohol, equal to a 12 oz beer at 5%, 5 oz of wine at 12%, or 1.5 oz of 40% spirits [15]. See theNIAAA’s standard drink pagefor more.
When the results may be wrong
- Misread hydrometers (read at the bottom of the meniscus), bubbles clinging to the hydrometer, or uncorrected sample temperature.
- Sugar added after the OG reading (priming sugar, fruit, honey or step feeding) without adding its gravity to OG.
- Refractometer estimates for low-attenuation beers, or wort correction factors far from your instrument’s real value.
- Cocktail dilution, which is always a rough guide.
All ABV formulas here are approximations. Commercial producers who must state ABV on a label use lab methods instead.
Common questions
How do you calculate ABV from gravity readings?
Subtract the final gravity from the original gravity and multiply by 131.25. A beer from 1.062 to 1.012 is (0.050 × 131.25) ≈ 6.6% ABV. Above about 8%, the alternate formula above is usually more accurate.
Can I work out ABV without an original gravity reading?
Not reliably. Both formulas need the gravity before fermentation. If you used a recipe kit, its expected OG gives a rough estimate, but the result is only as good as that guess.
Can I use a refractometer for final gravity?
Yes, but not directly. Once alcohol is present the raw reading is too high, so you need the original reading and a correction formula like the one in the Refractometer tab.
What’s the difference between ABV and ABW?
ABV is the share of the drink’s volume that is alcohol; ABW is the share of its weight. Because alcohol is lighter than water, ABW is lower, about 0.79 times ABV for beer.
How strong is a cocktail after shaking or stirring?
Weaker than the ingredients alone suggest. A sour made with 2 oz of 45% whiskey and 1.5 oz of juice and syrup is about 26% before ice and roughly 15–16% after shaking, based on Arnold’s measured dilution.
Sources
- Brewer’s Friend, “Alcohol By Volume Calculator Updated” (2011)Standard and alternate ABV formulas, with worked example
- Homebrew Academy, “ABV Calculator”Standard and alternate ABV, ABW, real extract and calories per 12 oz, with worked example
- BeerSmith, “Apparent and Real Attenuation for Beer Brewers – Part 1” (2010)Apparent attenuation formula, with worked example
- The Oxford Companion to Beer, “calories” (via Craft Beer & Brewing)Calorie method (6.9 kcal/g alcohol, 4 kcal/g extract, ash, × 3.55 for 12 oz)
- Brew Your Own, “Counting Calories & Carbs”Real extract and calorie method; ABW ≈ 0.79 × ABV
- Brewer’s Friend, “Plato to SG Conversion Chart”SG ↔ °Plato formulas; Brix ≈ Plato for brewing
- Craft Beer & Brewing, “Specific Gravity or Just a Matter of Degree?” (2016)Brix, Plato and Balling are functionally equivalent at home
- Calculator Academy, “Hydrometer Correction Calculator”Hydrometer temperature-correction formula, with worked example
- Homebrew Academy, “Hydrometer Temperature Correction Calculator”Same correction coefficients; 59 °F vs 68 °F calibration
- Brewer’s Friend, “Hydrometer Temperature Correction”Typical calibration temperatures; 32–159 °F input range
- Sean Terrill, “Refractometer FG Results” (2011)Cubic final-gravity correlation; data excluded beers below ~61% apparent attenuation
- Sean Terrill, “Refractometer Calculator” (2012)Wort correction factor (default 1.04; typically 1.02–1.06) applied by dividing readings
- Lacada Brewery, “Refractometer Correction Calculator”Independent statement of the same cubic and correction factor
- Dave Arnold, “Cocktail Science in General: Part 2 of 2,” Cooking Issues (2010)Measured dilution: ~50% for a stirred Manhattan, ~63% for a shaken whiskey sour
- NIAAA, “What Is A Standard Drink?”US standard drink = about 0.6 fl oz (14 g) of pure alcohol
The formulas were checked against these published sources and their worked examples, which are part of this calculator’s automated tests. This page doesn’t give health or legal advice.