An ABV calculator tells you how much alcohol is in a finished beer from two hydrometer (or converted refractometer) readings: original gravity (OG) and final gravity (FG). Homebrewers, brew-day notes, and competition entries all use alcohol by volume because it is the number on a commercial label. This free beer ABV calculator supports specific gravity and Plato, the standard homebrew equation, the alternate Hall formula for high-gravity beers, apparent attenuation, and calories per 12 oz.
Use the tool above first, then keep reading for the formulas, a worked example, and the measurement mistakes that make two brewers report different ABVs for the same batch.
How to calculate beer ABV from OG and FG
Measure original gravity of the wort before fermentation. After yeast finishes, measure final gravity before priming sugar. Subtract FG from OG and scale the difference. Temperature-correct hydrometer samples. If you used a refractometer after alcohol is present, do not treat raw Brix as FG — ethanol skews the reading.
- Enter original gravity (OG) to match your instrument (SG such as 1.050, or °Plato).
- Enter final gravity (FG) after fermentation is stable.
- Choose the standard formula for everyday strengths or the alternate (Hall) formula when OG is high.
ABV formulas this calculator uses
The standard alcohol by volume formula is the one most homebrewers memorize:
ABV = (OG − FG) × 131.25Example: OG 1.050 and FG 1.010 → (1.050 − 1.010) × 131.25 = 5.25% ABV. Session ales, pale lagers, and most house beers sit in this range, so the standard equation is usually enough.
For bigger beers, Dr. Michael Hall’s alternate equation (often cited from Zymurgy) accounts for the changing relationship between extract and alcohol:
ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794)The same 1.050 / 1.010 example is about 5.34% ABV. The gap widens on imperial stouts, barleywines, and other worts much above 1.070 OG. Switch formulas in the calculator when you are packaging a high-gravity beer, not because one equation is “more official” for every style.
Apparent attenuation and calories per 12 oz
Apparent attenuation estimates how much sugar yeast consumed: (1 − FG°P / OG°P) × 100. With OG 1.050 and FG 1.010 that is about 79%. A healthy attenuation number is a fermentation check; it is not a second ABV.
Calories per 12 oz follow the ASBC Beer-33 approach (real extract plus alcohol by weight). The same sample is about 163.7 calories per 12 oz. Calorie math does not change when you toggle standard vs Hall ABV.
Original gravity, final gravity, SG, and Plato
Original gravity is the density of wort before fermentation — a snapshot of available sugars and potential alcohol. Final gravity is density after fermentation: a lower FG is a drier beer; a higher FG leaves more residual sweetness and body. Specific gravity compares density to water (1.050). Degrees Plato (°P) express dissolved solids as a percentage by weight. This OG FG calculator converts between both so you can match a hydrometer scale or a Plato lab reading without doing the conversion by hand.
Alcohol by volume is the percent of the finished beer that is ethanol by volume. If two people get different ABVs, the usual cause is the sample (hot wort, uncorrected hydrometer, priming sugar in the FG sample), not a rounding difference of a few hundredths of a percent.
ABV calculator FAQ
How do you calculate ABV from OG and FG?
The standard formula is ABV = (OG − FG) × 131.25, where OG and FG are specific gravity readings. For higher-gravity beers, the alternate Hall formula is usually more accurate.
What is a good ABV for beer?
Most session beers are about 3–5% ABV, standard ales and lagers 4–6%, and stronger styles like IPA, Belgian tripels, or imperial stouts often range from 7–12%+ ABV.
Should I use Specific Gravity or Plato?
Use whichever unit your hydrometer or refractometer reports. CalculatorMint converts between SG and °Plato automatically and shows both in the results.
When should I use the alternate ABV formula?
Use the alternate (Hall) equation for high-gravity beers, especially above roughly 1.070 OG / 8% ABV. For everyday homebrew strengths, the standard formula is fine.
For brew-day traps in more depth, read How to calculate beer ABV from OG and FG.