Originally Posted by OneCerebralSamurai
I use the calculator on this site:http://www.brewersfriend.com/abv-calculator/
Make sure you check the button for the "Alternate" equation as it gives more accurate results, particularly at higher OGs.
Your numbers come out to 13.26% abv
BTW the "standard" equation on the site is ABV = (og fg) * 131.25
The "Alternate" (better) equation is ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)
Actually, the alternate equation looks like it gives erroneous reading that are seriously too high. If you use the fundamental chemistry as outlined HERE
the calculation will give you a little above 12%.
As a example of where this "improved" equation breaks down, try assuming a high-gravity fermentation with SG 1.135 and FG 1.000. If you plug that in the equation, you get an ABV of 20.21%. The standard equation give you 17.72%. Using the methodology outlined on howstuffworks, you get 17.94, and if you use a calculator like vinocalc
you get 18.6. In order to arrive at 20.21% you have to assume that there is 100% conversion of the 354 grams per liter of sugar into ethanol and that is simply unrealistic. While all of these calculation are estimates, and can be off due to amount of alcohol scrubbed off through entrainment with CO2 (a bigger percentage at high temps) and due to amounts converted into other things like glycerol and higher alcohols, this "improved" formula is just more "off" than some of the others.
Having run some high gravity batches like this, I have measured the ABV using spirit indication with fine scale hydrometers and once sent a sample to a lab, and at a starting gravity of 1.135 I've never measured 20% ABV.