To calculate how much alcohol is present in your brew, you simply need to compare the gravity readings taken from before and after the fermentation. The results are shown in both ABV (Alcohol by Volume) as well as ABW (Alcohol by Weight). In general, we display recipe information using ABV.
Alcohol by VolumeABV is generally international standard for measuring how much alcohol is contained in a beverage. It simply means what percentage of a given amount of a liquid is alcohol. Technically ABV is definied as the number of milliliters of pure ethanol present in 100 milliliters of a solution, at 20°C
Alchohol by WeightABW is occasionally used instead of ABV. ABW differs from ABV in that it is based on the percentage of alcohol in a total mass of a liquid. At lower levels, ABW is about 4/5 of the ABV (eg. 3.5% ABW = 4.6% ABV), but that changes as the percentage of alcohol increases.