Last Updated on 14.07.11 Written by Keith
When brewing your beer, before pitching the yeast, use your hydrometer and take a gravity reading at 20°c, it will be around 1.040 this is called the OG or Original Gravity. Then once the brew is done fermenting take another gravity reading, it should be around 1.008, this is called the FG or Final Gravity. Then using the formula (OG - FG) x 131 = ABV%. This should give you a close approximation of the alcohol by volume. In the case of the above numbers this would be just shy of 4.2%.