Alcohol By Volume (ABV) Calculator

Specific gravity (SG) is the density of a liquid compared to pure water at the same temperature. Water has an SG of exactly 1.000. Sugar dissolved in wort raises the density, so a typical pre-fermentation original gravity (OG) reads 1.040 to 1.080. As yeast convert sugar to alcohol and CO2, density drops, and a final gravity (FG) of 1.008 to 1.020 is normal for most beer styles. The difference between OG and FG is the input every ABV formula needs.

A hydrometer is a sealed glass float with a weighted bulb and a calibrated stem. You drop it into a test sample of your wort and read where the liquid surface crosses the stem. The denser the liquid, the higher the hydrometer floats, which corresponds to a higher gravity reading. Most brewing hydrometers are calibrated to 60 F (15.5 C) or 68 F (20 C), so adjust the reading if your sample is significantly warmer or colder. A refractometer reaches the same answer with a single drop, but its readings get distorted by alcohol, so most brewers still verify FG with a hydrometer.

The simple option uses (OG - FG) x 131.25. The advanced option uses the longer gravity-ratio equation and is the calculator's default. The alternative option uses the Miller-style equation. All three estimate ABV from two gravity readings and can diverge as gravity increases. Use one method consistently for batch comparisons, and use a laboratory measurement when the exact alcohol content matters.

Apparent attenuation, (OG - FG) / (OG - 1) * 100, is the percentage of sugars the yeast appears to have fermented, calculated straight from gravity readings. It runs high because ethanol is less dense than water, so it pulls FG down further than the sugar reduction alone would. Real attenuation is roughly apparent attenuation * 0.81 and represents the actual percent of sugars the yeast consumed. A typical ale finishes at 75% apparent and about 60% real attenuation. Pro brewers and yeast labs publish both, but apparent is what you see on a homebrew hydrometer.

US proof is twice the ABV. A beverage at 5% ABV is 10 proof, and a spirit at 40% ABV is 80 proof. This calculator returns ABV rather than a separate proof field. It also shows pure alcohol and US standard-drink equivalents for a 12 fl oz serving.