% ABV = (SGf – SGi)/0.0074, where SGf is the final specific gravity and SGi is the initial specific gravity.

For example, if the initial specific gravity was 1.110 and the final value was 0.996, the calculated alcohol content would be 15.4%. But what if you forgot to get the initial specific gravity? The specific gravity can be calculated from the Brix number only in the absence of alcohol. However, if one measures the Brix number AND the specific gravity after fermentation, the %ABV can be calculated from the following formula:

% ABV = (1.646*Brix) – (2.703*(145-145/SG)) – 1.794

The easiest way to do this routinely is to use an Excel spreadsheet. For example, in cell C1 enter the Brix value (=Brix). In cell C2, enter the SG (=SG). Then in cell B7, enter (copy and paste):

**=1.646*C1-(2.703*(145-145/C2))-1.794**

This will be the final %ABV. You can label the cells appropriately for use, such as “Brix” next to cell C1, “SP” next to cell3, and “%ABV” next to cell B7.

The spreadsheet makes the calculations very straightforward and easy.