A session beer is defined as a beer with an alcohol by volume or ABV of less then 5%. The purpose of a session beer is to permit the drinker to enjoy multiple beers at a sitting without becoming overly intoxicated.
The final gravity or FG of a beer is the beer’s specific gravity once fermentation has completed. Once a brewer has measured the final gravity, it can be compared to the original gravity and the ABV or alcohol by volume can be calculated. The final gravity of a beer is typically taken using a hydrometer or refractometer. Specialty final gravity hydrometers are available to allow you to take a more accurate reading of your final gravity if desired.
Below are three different types of hydrometers used for taking the specific gravity readings of beer.
Alcohol by volume (ABV) represents what portion of the total volume of a liquid is alcohol.
To calculate the ABV of a beer, you will want to subtract the Final Gravity from your Original Gravity and multiply by 131.
The following is an example of how to calculate your alcohol by volume, assuming that your original gravity was 1.055 and your final gravity reading was 1.012.
Here is an example: 1.055 – 1.012 = 0.043 x 131 = 5.633%
In this example your alcohol by volume worked out to 5.633%.