🍺ABV Calculator

About this tool

Enter your original gravity (before pitching the yeast) and final gravity (when fermentation has finished) as specific gravity or Brix/Plato. You'll see the ABV, which formula was used, the apparent attenuation and the gravities. Tick temperature correction if your samples weren't at the hydrometer's calibration temperature.

How homebrew ABV is calculated

Yeast turns sugar into roughly equal weights of alcohol and carbon dioxide. Sugar makes the liquid denser and alcohol makes it lighter, so the drop in specific gravity between the start and the end of fermentation shows how much alcohol was made. The standard homebrewing formula is ABV = (OG − FG) × 131.25, so a beer that starts at 1.050 and finishes at 1.010 is about 5.25%. Above about 7% that simple formula underestimates, so the calculator switches to the alternative formula, ABV = 76.08 × (OG − FG) ÷ (1.775 − OG) × FG ÷ 0.794. A 1.090 to 1.015 barley wine comes out at about 10.6% instead of 9.8%. Apparent attenuation, (OG − FG) ÷ (OG − 1), shows how much of the sugar was fermented: 80% here, typical for an ale yeast. Hydrometers are calibrated at 60 °F (15.6 °C) or 20 °C, and a warmer sample reads low, so a reading of 1.050 at 80 °F is really about 1.052. Refractometers read in Brix and are fine for the original gravity, but alcohol distorts readings once fermentation starts, so use a hydrometer for the final gravity. Honest limits: these are estimates good to a few tenths of a percent. Priming sugar at bottling adds roughly 0.3–0.4%, only a lab test is exact, and selling alcohol requires accurate, legally compliant labels. Please drink responsibly. The alcohol units calculator and the unit converter are related.

Frequently asked questions