Originally Posted by Pogo
If the Original Gravity (OG) of your batch is 1.071, and the Final Gravity (FG) turns out to be, say, 0.998.
To estimate the Alcohol By Volume (ABV), simply subtract the FG from the OG, and multiply the result by 131.
(OG - FG) X 131 = % ABV
1.071 - 0.998 = 0.073 X 131 = 9.563 % ABV
I always used this for final ABV.
OG-FG/7.36*1000 = %ABV
1.071 - 0.998 = 0.073 / 7.31 = 0.00998 * 1000 = 9.98 ABV.
Forget the fact that its a little more math. I have seen both formulas use. Is there a way to tell which is better or closer to the actual?
In addition the "Joy of Homebrewing" (AKA the BIBLE as some people say) says the equation is og-fg x 105, as brewmonkey says og-fg x 131.
Fermcalc says OG 1.071 - FG 0.998 = 9.9 %ABV