Beer ABV Calculator
Determine alcohol by volume, apparent attenuation, and calories from hydrometer gravity readings.
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How Beer ABV and Attenuation Work
Specific gravity indicates the density of liquid relative to pure water (1.000). Wort gets its density from fermentable and unfermentable sugars extracted from malted grains. During fermentation, yeast consumes sugars and releases ethanol (density ~0.789) and carbon dioxide gas.
Because ethanol is significantly less dense than water, gravity drops as alcohol increases. The standard formula ABV = (OG - FG) * 131.25 calculates the volume percentage of alcohol produced. For high-gravity wort (OG > 1.060), ethanol's density depression becomes non-linear, making Hall's equation more accurate.
Frequently Asked Questions
What is the standard formula to calculate homebrew ABV?
The standard brewing formula is ABV = (Original Gravity - Final Gravity) * 131.25. For example, an OG of 1.055 and FG of 1.012 yields (1.055 - 1.012) * 131.25 = 5.64% ABV.
When should I use Hall’s high-gravity equation?
For beers above 1.060 OG (such as Double IPAs, Imperial Stouts, and Barleywines), ethanol density decreases the hydrometer reading non-linearly. The Hall formula corrects for this expansion.
What is normal yeast attenuation?
Most standard ale yeast strains attenuate between 72% and 82%. Saisons with diastaticus yeast can exceed 88% to 95%, while English ale yeasts often finish sweeter at 68% to 74%.