Calculating Beer Alcohol Content

Question

I just want to confirm that I am calculating alcohol by weight correctly. My starting gravity was 1.051 and my final gravity was 1.012 (51-12=39) is that 3.9% or do i have to then multiple it by 1.3?

Answer

The equation is {[(1.05)*(OG – FG)]/FG} * 100

where OG and FG are the original and final gravities respectively written out in their complete form (e.g. 1.051).

In your case {[(1.05)*(0.039)]/1.012} * 100 = 4.05% alcohol by weight.

To determine the percent alcohol by volume simply divide the by weight value by 0.79.

In your case that would be 5.1%.