How to Calculate ABV From Specific Gravity

ABV, alcohol by volume, is the standard way to measure the alcohol content of beer or wine. Simply stated, it's the volume of ethanol (alcohol) in a liquid divided by the total volume of liquid. For instance, if a 750 cubic-centimeter bottle contains 75 cubic centimeters of ethanol, the liquid is 10% alcohol by volume. ABV is expressed as a percentage.

Brewers, distillers and vintners measure alcohol content by comparing the specific gravity of the liquid before and after fermentation, in which yeast eats the sugar and replaces it with carbon dioxide and ethanol.

Things You'll Need

Hydrometer

Thermometer

Instructions

Measure the specific gravity of the unfermented liquid with a hydrometer. This measurement must be made at a standard temperature, usually 60 degrees Fahrenheit. Record this value, which is called the "original gravity" or OG.
Pitch the yeast and allow the liquid to ferment. This takes from several days to several weeks, depending on the spirit being made.
Measure the specific gravity of the liquid with the same hydrometer after fermentation is complete. Again, measure the specific gravity at standard temperature of 60 degrees Fahrenheit. Record this measurement, termed the final gravity (FG).
Calculate the ABV. Subtract the final gravity from the original gravity and multiply the difference by 131. For example, if OG = 1.085 and FG = 1.016, multiply the difference (0.069) by 131 to get an ABV of very slightly over 9, for an ABV of 9 percent.

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