ABV

ABV, or alcohol by volume, is the percentage of a finished beer's volume that is actually ethanol. Homebrewers cannot measure alcohol directly without lab equipment, so ABV is instead estimated using the two gravity readings taken before and after fermentation, since that drop reflects how much sugar the yeast converted into alcohol and CO2.

The most common home method multiplies the difference between original gravity and final gravity by a constant, often around 131 to 132, to get an approximate percentage. It is not a lab-precise figure, but it is consistent enough to compare batches, plan a recipe's strength, or decide if a beer landed close to style guidelines. Simple online or app-based calculators handle the math from your two readings so you do not have to do it by hand.

A common confusion is treating the ABV estimate as exact rather than approximate, since factors like calibration of your hydrometer, sample temperature, and the specific formula used can shift the result slightly. Another mistake is calculating ABV from a final gravity that has not actually stabilized, which inflates the apparent alcohol content because fermentation was still active. Always confirm FG is steady before trusting the ABV number.