Which formula is used to calculate ABV?

The formula used to calculate Alcohol by Volume (ABV) in brewing is derived from the difference between the original gravity (OG) and final gravity (FG) of the beer. Specifically, the equation (OG - FG) * 131.25 provides an estimate of the percentage of alcohol in the finished beer.

Original gravity refers to the specific gravity of the wort before fermentation, which indicates the sugar content that yeast will ferment into alcohol and carbon dioxide. Final gravity measures the specific gravity of the beer after fermentation, indicating how much sugar has been converted to alcohol. By subtracting FG from OG, brewers can determine the amount of sugar that has been fermented into alcohol. Multiplying this difference by 131.25 converts the gravity difference into a percentage, yielding the ABV.

This understanding enables brewers to monitor alcohol content and make adjustments in the brewing process. Other formulas such as (FG + OG) or variations involving division are not applicable for calculating ABV and do not correctly reflect the fermentation process.