# Estimating final alcohol by Original Gravity

Is it possible to estimate final alcohol value from the orginal gravity of the wort? Is apparent attenutaion involved in the estimation?

I guess if I know OG and FG this is the answer. What if FG is not know?

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MalFet's answer is good, but at the end of the day, it's still an estimate and open to a reasonable error range. If you have experience in tasting beers, you may be able to draw on that to work out whether the estimated FG is in the ballpark. However, if you don't have much room for error, you should buy a hydrometer and actually measure the FG. – tallie Mar 12 '13 at 0:44
Also if you don't have a measurement of OG you may be off on that to. Best to get a hydrometer and measure both if you aren't already. – Chris Plaisier Mar 12 '13 at 18:24

Alcohol is the product of anaerobic respiration, the consumption of sugars by yeast. If you had access to a chemistry lab, you could measure the alcohol directly, but most calculate their alcohol by calculating the quantity of sugar that has been consumed. For the most part, this is done by comparing the OG to the FG.

In other words, the OG by itself will not tell you how much alcohol there is. You need to either measure or estimate the FG. If measuring is not an option, you can use your expected attenuation to estimate it.

FG = (OG - 1.000) * (apparent attenuation) + 1.000

From there, you can use any of the ABV estimation formulas.

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Could you give an worked example with some numbers? – Cleber Goncalves Mar 11 '13 at 17:02
If your OG is 1.080, and you get 75% attenuation, your FG should be (1.080 - 1.000) * (.75) + 1.000 = 1.020. – MalFet Mar 11 '13 at 17:39
I'm fairly certain alcohol is produced via aerobic respiration, otherwise aerating the wort would be counter-productive. Secondary fermentation should be anaerobic, hence it typically being done in a glass carboy to ensure no oxygen can permeate the vessel. – thesquaregroot Nov 27 '15 at 12:53
Ah, nevermind, it seems oxygen is important to yeast growth, not the fermentation itself. Alcohol production is in fact anaerobic. – thesquaregroot Nov 27 '15 at 13:22