% Alcohol content ?

[Seven7]

Hi,
I was wondering what is your best technique to calculate the % of alcohol?
Because So far I found 4 different techniques and all of them give me a different %!

If I take my latest gravity:
initial: 1.043
final: 1.008

1) Hydrometer instructions (reference attachment) : initial (5.19) - final (-1.18) = 6.37%
2) Cooper Cans: (1043 - 1008 ÷ 7.46) + 0.5 = 5.19%
3) http://www.brewersfriend.com/abv-calculator/ = 4.59%
4) Alcohol Calculator (free iPhone app) = 4.65%
https://itunes.apple.com/ca/app/alcohol-calculator/id364030199?mt=8

I also have a friend at work who has a different technique and it gives also a different result (i will update later)

What technique are you using ?
... and is there a way to really know it the right % or to close

Cheers,

 

[Qhrumphf]

At the end of the day, only way to truly know the ABV is via a lab test. Like IBU calculations, they're all an estimate. I use two, a short one for quick estimates, and a long one that I use for note taking purposes. ABV = (OG-FG) * 131.25 is the short one, and the long one ABV = (76.08 * (og-fg) / (1.775-og)) * (fg / 0.794). You can use both equations via the Brewer's Friend link above. At moderate gravities they're very close. Once you get high gravity (and high ABV) the differences between the two get pretty major (more than a percentage point once you get above 10%).

 

[Seven7]

i dont know other techniques to calculate the %
my problem is it goes from 4.5 to 6.5% difference
... is there a better way to know the % ?

Another one:
http://www.rooftopbrew.net/abv_calculator.php
result 4.7%

 

[Qhrumphf]

The more commonly used ones all agree it's in the ~4.5% range. You won't get better than a guess, but that's going to be about right. The only way you'll do better is with a lab actually chemically measuring the alcohol level (and then, if you want, charting it and coming up with your own formula). If you're really worried, you can send out a sample (I believe White Labs offers tests for both IBUs and ABV to homebrewers, among other tests, if not, I'm sure someone else does) but it'll cost you.

 

[Yooper]

The easiest (and closest) estimate is just doing the math. The simple formula is (OG-FG) x 131 = approx ABV.

So, in your example of 1.043 and 1.008, I come up with 4.585% ABV.

With an OG of 1.043, there is no possible way for your ABV to be at 6%, so you can throw what whatever gave you that estimate. 4.5%-4.6% is right in the neighborhood.

 

[ColeVet67]

this is what i use.. (OG-FG) x 131.25 = approx ABV

 

[unionrdr]

I've seen some 8 different formulas, but I use the Cooper's formula of (OG-FG) / 7.46 + .5 = ABV%. It's at the high-side answer-wise, but I've found it to be with the range Beersmith 2.1 gives. I got 5.192% to be more exact.

 

[Talgrath]

The more commonly used ones all agree it's in the ~4.5% range. You won't get better than a guess, but that's going to be about right. The only way you'll do better is with a lab actually chemically measuring the alcohol level (and then, if you want, charting it and coming up with your own formula). If you're really worried, you can send out a sample (I believe White Labs offers tests for both IBUs and ABV to homebrewers, among other tests, if not, I'm sure someone else does) but it'll cost you.

http://www.whitelabs.com/other-products/tk2300-beer-analysis-sample-kit

Yep, their basic tests give you ABV and IBUs, when you go to the site to fill out the information for your sample label you can purchase additional tests (such as color).