ABV Calculator

In short Alcohol by volume comes from the gravity a wort started at and the gravity it finished at, and there are three published ways to get from one to the other. The one everybody memorises is (OG − FG) × 131.25, which for a beer that went from 1.050 to 1.010 gives 5.25%. The alternate formula gives 5.34% and the Balling route, which is what commercial brewers use, gives 5.29%. At 1.050 that spread is under a tenth of a percentage point — less than a hydrometer can resolve — so it does not matter which you take. It grows with gravity though, and by 1.070 it is already about a third of a point. IT STARTS TO MATTER ABOVE ABOUT 1.070. The simple formula assumes a fixed relationship between the gravity drop and the alcohol produced, and that assumption weakens as the wort gets stronger. Take a big beer from 1.090 to 1.020 and the three methods give 9.19%, 9.99% and 9.45% — three quarters of a percentage point apart, which is the difference between a strong ale and a barley wine on a label. This page shows all three rather than averaging them, because averaging three approximations produces a fourth number that nobody published. APPARENT AND REAL ATTENUATION ARE BOTH LEGITIMATE AND THEY ARE NOT THE SAME. A hydrometer floats in a liquid that now contains alcohol, and alcohol is lighter than water, so the final reading comes out low and the attenuation looks better than it was. That 1.050 to 1.010 beer shows 80% apparent attenuation and about 65% real. Yeast suppliers quote the apparent figure, which is why a strain advertised at 75% is genuinely converting about 61%. Neither number is wrong; they answer different questions. Two limits worth stating. A home hydrometer reads to about one gravity point, which is roughly 0.13% ABV, so quoting ABV to two decimals is arithmetic outrunning measurement. And most hydrometers are calibrated at 20°C and read low in warm samples, which is a bigger error than the choice of formula.