If you want to know the alcohol percentage or ABV of your beer, take an SG reading using your hydrometer before fermenting (original gravity (OG)) (see reading SG below) and then another after the beer is ready to be bottled, (Final Gravity (FG)). To calculate the percentage of beer, simply put your OG and FG into the following equation:
ABV = (OG-FG) x 131
ABV = (1.056-1.014) x 131
ABV = .042 x 131= 5.502%
This is not an exact calculation as there are other factors involved. If the OG is lower, then the multiplier reduces. If calculating a beer with a start gravity of under 1030 then use 125 as a more appropriate multiplier.