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ckwatson · 03-21-2011, 04:05 AM

I have some questions about figuring out my alcohol content. When I use my specific gravity and do the math (OG-FGx105) gives me a ABV of 3.57 when I use the alcohol scale from my hygrometer it gives me a reading of 4.5 (6.5%-2%) Is this normal?

**AZ_IPA** · 03-21-2011, 04:07 AM

The formula used by most is:

OG-FG x 131...

**Arneba28** · 03-21-2011, 04:08 AM

(OG-FG)x 131. thats what I was always told?

**Yuri_Rage** · 03-21-2011, 04:12 AM

The alcohol potential scale on your hyDrometer is probably less precise than the specific gravity scale, so using a formula to calculate ABV from specific gravity is likely the best way to get good results.

The formula you're using is for approximating alcohol by weight (ABW). The ones posted above are correct for alcohol by volume (ABV).

ckwatson · 03-21-2011, 04:31 AM

Thanks for the heads up on the ABW, when I use 131 I get very close to the 4.5% from the alcohol potential scale.

Captain Damage · 03-21-2011, 09:57 AM

The potential alcohol scale on your hydrometer is intended for winemakers. It doesn't work for beer with it's proteins and unfermentables.

**beergynt** · 03-27-2011, 05:27 PM

I think that OG-FGx105 was stated in Papazian's book... I tried it and soon found it to be wrong. I wound up playing with the numbers and comparing them to Beersmith's figures until I settled on 130, but I'm sure 131 is right there...

Calder · 03-27-2011, 09:05 PM

Both are correct.

x 105 will give you the percentage of alcohol by weight in the beer.

x 131 will give you the percentage of alcohol by volume in the beer.

**unionrdr** · 03-27-2011, 10:08 PM

I've been using the formula in the Cooper's directions. OG-FG/7.46 + .5= approximate %ABV.

Calder · 03-28-2011, 12:29 AM

Quote:

Originally Posted by unionrdr

I've been using the formula in the Cooper's directions. OG-FG/7.46 + .5= approximate %ABV.

Time to change. Check out a few web sites for calculators and you will see which is correct.