Beer Brewing ABV Calculator

Alcohol by volume tells a homebrewer how potent a finished beer turned out, and it shapes everything from recipe design to quality control. Pinning the number down lets you confirm a batch hit its target, compare it against the style you were aiming for, and steer your next brew day with confidence rather than guesswork.

The estimate rests on the gap between two gravity readings: original gravity (OG) before fermentation and final gravity (FG) after. The widely used formula ABV = (OG - FG) * 131.25 turns that difference into an alcohol figure, with both readings taken on a hydrometer. It gives a dependable read on how much sugar the yeast converted. Calories per 12 oz come from the same two readings: both are converted to degrees Plato, the real extract and alcohol by weight are derived from them, and the ASBC formula adds 6.9 calories per gram of alcohol to 4 per gram of remaining carbohydrate, about 164 calories for 1.050 to 1.010.

Temperature is where accuracy lives or dies, so take every gravity reading at the same temperature; drift there skews the hydrometer. Pull the final reading too early, before fermentation has truly finished, and you'll undershoot the real ABV. Treat the output as a solid estimate, not a lab measurement, since pinpoint accuracy calls for laboratory analysis.