ABV Calculator (Alcohol By Volume)
Wondering how strong your homebrew turned out? Enter your original gravity (before fermentation) and final gravity (after fermentation) to calculate the alcohol content, attenuation, and estimated calories.
The standard ABV formula used by homebrewers is: ABV = (OG - FG) x 131.25. This takes the difference between your original gravity (OG) and final gravity (FG) and converts it to a percentage of alcohol by volume.
For example, a beer with an OG of 1.050 and FG of 1.010 has an ABV of (1.050 - 1.010) x 131.25 = 5.25%. That puts it right in the range of a typical American pale ale.
Apparent attenuation tells you what percentage of the original sugars the yeast converted. Most healthy fermentations hit 70-80% attenuation. Below 65% might mean the fermentation stalled, while above 85% indicates a very dry beer. Different yeast strains have characteristic attenuation ranges -- a Belgian strain might push 85%+ while an English ale yeast might settle around 72%.
The 131.25 constant comes from the mathematical relationship between specific gravity units and the density change caused by ethanol replacing sugar in solution. For very high-gravity beers above 8% ABV, some brewers prefer the more precise alternate formula: ABV = (76.08 x (OG - FG) / (1.775 - OG)) x (FG / 0.794), which accounts for non-linear effects at higher alcohol concentrations.