Need help with ABV%

[dlabrie]

I just finished bottling a nut brown ale that I made from a partial grain kit.

The OG before pitching the yeast was 1.058. The FG before adding sugar was 1.028 on a hydrometer and 7 Brix on a Refractometer.

If I go to Andy's ABV Calculator and plug in the two SG readings, adjusted to 68 degrees, I get an ABV of 4%.

If I go to Onebeer.com and complete the Corrected Final Gravity & ABV% by Brix table, using 14.26 brix for the 1.058SG OG and 7Brix for the FG I get 6.47%ABV.

Which is correct? Am I doing something wrong?
Thanks.

 

[cluckk]

((1.058-1.028)*1.05)*1.25=3.93%abv.

The brix from the refrac after fermentation is not accurate.

 

[cluckk]

OG-FG then multiply by 105 gives you ABW. Alcohol weighs less than water so multiply by 1.25 to get ABV.

The refractometer uses the refraction of light through the liquid. Alcohol refracts differently than water, so the alc throws it off.

 

[dlabrie]

((1.058-1.028)*1.05)*1.25=3.93%abv.

The brix from the refrac after fermentation is not accurate.

I thought that this site took that into consideration.
It says---
Refractometers are a great way to sample gravity, however once alcohol is created during fermentation they will require a few calculations to correct the reading. The calculators below will convert Orignal Brix to Original Gravity (pre fermentation only) and will convert Original/Final Brix to Final Gravity and ABV% (during and post fermentation) without the need to use a hydrometer.

Is 4% about right for a nut brown?