ABV Calculator

Fermentation converts sugar into alcohol and carbon dioxide, and the density of a fermenting liquid drops as that conversion happens -- sugar is denser than the alcohol it becomes. That's why home brewers and winemakers track two hydrometer readings: Original Gravity (OG), taken before fermentation starts, and Final Gravity (FG), taken once it's finished. This calculator applies the widely-used simplified ABV formula, (OG - FG) x 131.25, a linear approximation that home brewing references commonly cite as accurate to within about 0.3 percentage points of ABV for original gravities up to roughly 1.070 (a typical beer strength), though it's known to drift further from lab-measured ABV at the higher original gravities used for barleywines, imperial stouts, and other big, high-alcohol styles.

A higher Original Gravity always raises the resulting ABV, since it represents more sugar available to ferment into alcohol, while a higher Final Gravity always lowers ABV, since it means more unfermented sugar remained in the liquid. Final Gravity is actually the stronger lever on Apparent Attenuation -- the percentage of available sugar that fermentation actually converted -- because Apparent Attenuation compares how far FG dropped relative to the distance from OG down to 1.000 (pure water), and FG sits closer to that reference point across the calculator's typical ranges. ABW (Alcohol By Weight) is simply ABV scaled by ethanol's density relative to water, and the Calories estimate factors in both the alcohol produced and the residual (unfermented) extract left behind in the final liquid.