About this tool
The ABV Calculator is a free, in-browser homebrewing tool that turns your original gravity (OG) and final gravity (FG) readings into the finished alcohol content of your beer, wine, mead, or cider. Enter the two specific-gravity numbers from your hydrometer or refractometer and it returns alcohol by volume (ABV), alcohol by weight (ABW), apparent and real attenuation, and the calorie count of a serving. Everything runs locally in your browser, so nothing you enter is uploaded.
Two ABV methods are shown. The quick estimate is ABV% = (OG − FG) × 131.25, which is accurate for typical session and pale beers. The default headline figure uses the more accurate high-gravity formula ABV% = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794), which better tracks strong beers and wines where the simple constant drifts. Alcohol by weight is ABW% = ABV% × 0.79336. Apparent attenuation — how much of the sugar the yeast consumed — is (OG − FG) / (OG − 1) × 100, and real attenuation is 0.8192 × apparent. Calories per 12 oz are the sum of an alcohol term, 1881.22 × FG × (OG − FG) / (1.775 − OG), and a carbohydrate term, 3550 × FG × (0.1808 × OG + 0.8192 × FG − 1.0004), scaled to your serving size.
As a worked example, a beer with OG 1.050 and FG 1.010 has a simple ABV of about 5.25%, an advanced ABV of about 5.34%, roughly 80% apparent attenuation, and about 165 calories in a 12 oz glass. Take gravity readings at the same temperature (or apply a hydrometer correction), and remember that refractometer readings need an alcohol correction once fermentation starts, since dissolved alcohol skews the reading.