How to calculate ABV?

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How to calculate ABV?

Postby helloworld » Fri Aug 08, 2014 3:41 pm

I have found equations online, but none have explanations or derivations, and that just bothers me. Does anyone know of a resource for where (OG-FG)*131.25 came from? 131.25 means nothing to me without an explanation, and I cannot find any supporting documentation. I looked in Palmer's and all I found was a chart (kind of surprising coming from a technical guy who collaborated with a JPL scientist). Thanks!
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Re: How to calculate ABV?

Postby Sqhead » Sat Aug 09, 2014 5:24 am

Here is what I use: OG minus FG x .129
Example: Og 1060 - fg 1010 is 50
50x.129 is 6.45 abv
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Re: How to calculate ABV?

Postby CA_Mouse » Sat Aug 09, 2014 6:54 am

Sqhead wrote:Here is what I use: OG minus FG x .129
Example: Og 1060 - fg 1010 is 50
50x.129 is 6.45 abv


Where did you get 129 from? Most ABV calculators use 131 as the multiplier (including our host's recipe sheets).

(OG - FG) * 131 = %ABV
(1.060 - 1.010) * 131 = 6.55%
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Re: How to calculate ABV?

Postby tookalisten » Sat Aug 09, 2014 12:58 pm

I have always heard it represents the change in gravity and is not a constant; but the 131 figure seems to be the most used middle of the road figure.
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Re: How to calculate ABV?

Postby CA_Mouse » Sun Aug 10, 2014 11:01 am

tookalisten wrote:I have always heard it represents the change in gravity and is not a constant; but the 131 figure seems to be the most used middle of the road figure.


Interesting... I've only seen 131 or 131.25. Perhaps it has a lot to do with your elevation, IE barometric pressure and elevation?
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Re: How to calculate ABV?

Postby pclemon » Mon Aug 11, 2014 4:49 am

CA_Mouse wrote:
tookalisten wrote:I have always heard it represents the change in gravity and is not a constant; but the 131 figure seems to be the most used middle of the road figure.


Interesting... I've only seen 131 or 131.25. Perhaps it has a lot to do with your elevation, IE barometric pressure and elevation?


Shouldn't - OG/FG are weight readings so unless you're on a different planet, gravity should be impacting all of that the same regardless of your elevation.

And before someone corrects me, yes, I know that there is less gravitational pull the further you get away from the center of the planet, but the difference between sea level and 15K feet would be so infinitesimal as to be a non factor.
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Re: How to calculate ABV?

Postby helloworld » Mon Aug 11, 2014 11:23 am

pclemon wrote:
CA_Mouse wrote:
tookalisten wrote:
And before someone corrects me, yes, I know that there is less gravitational pull the further you get away from the center of the planet, but the difference between sea level and 15K feet would be so infinitesimal as to be a non factor.


What if I'm brewing in a commercial airliner? Would the change in gravity be noticeable?

:D
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Re: How to calculate ABV?

Postby pclemon » Mon Aug 11, 2014 11:58 am

helloworld wrote:What if I'm brewing in a commercial airliner? Would the change in gravity be noticeable?

:D


Since the diameter of the earth is 8,000 miles and most commercial airlines fly, at most, at 6 miles (30K feet or so), I'd say no, nothing noticeable unless the plane goes into a parabolic dive and decreases the perceived gravity on you. :)
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Re: How to calculate ABV?

Postby CA_Mouse » Mon Aug 11, 2014 3:17 pm

pclemon wrote:And before someone corrects me, yes, I know that there is less gravitational pull the further you get away from the center of the planet, but the difference between sea level and 15K feet would be so infinitesimal as to be a non factor.


Well my wife and kids always complain that I start speaking an alien language when I start talking about beer..... hmmmmm :lol:
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Keg #2: Cascade Pale Ale
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Re: How to calculate ABV?

Postby MullerBrau » Mon Aug 11, 2014 3:37 pm

The calculation is probably not linear; that's why you see .128 or .131 or .13125 as a multiplier. If you are good at Excel, you could take a look at the spreadsheet that I use. It appears that the calculations for ABW are quite complicated and then for ABV, he uses a factor times ABW.

The spreadsheets are on my website and the password to unprotect is "beer"
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Re: How to calculate ABV?

Postby tookalisten » Mon Aug 11, 2014 5:17 pm

thats good security :D
Enjoy the little things, for one day you may look back and realize they were the big things.
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Re: How to calculate ABV?

Postby dmtaylor » Mon Aug 11, 2014 7:00 pm

MullerBrau wrote:The calculation is probably not linear; that's why you see .128 or .131 or .13125 as a multiplier.


Correct, it is a non-linear relationship. At low gravity, the multiplier is closer to 128. At high gravity, the multiplier is as high as 132 or so. In any case you can just use 130 or 131 all the time and get the right answer within 0.1% ABV.
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Re: How to calculate ABV?

Postby CA_Mouse » Tue Aug 12, 2014 1:56 am

I seem to learn some new math everytime I start exploring the "whats and whys" of how our hobby works. :shock:
Mouse
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That which does not kill us makes us stronger. - Friedrich Nietzsche


Primary: Hopping Dead
Secondary: Mead - Cinnamon; Boysenberry; Blackberry; Tart Cherry
Barrel #2: American Barleywine
Secondary: Dark Cherry Sour '13
Secondary: Pom-Cran Sour '13
Keg #1: Bourbon Barrel Oatmeal Stout
Keg #2: Cascade Pale Ale
Keg #3: Berliner Weiss
Keg #4: Cascade Pale Ale
Keg #5: Irish Red
Keg #6: Tart Walking IPA
Keg #7: Dad's Apple Cider
Bottled: Robin's Root Beer
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Re: How to calculate ABV?

Postby helloworld » Thu Aug 14, 2014 3:54 pm

MullerBrau wrote:The calculation is probably not linear; that's why you see .128 or .131 or .13125 as a multiplier. If you are good at Excel, you could take a look at the spreadsheet that I use. It appears that the calculations for ABW are quite complicated and then for ABV, he uses a factor times ABW.

The spreadsheets are on my website and the password to unprotect is "beer"



Excellent, thank you. I am an engineer and use Excel quite a bit.
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Re: How to calculate ABV?

Postby Sqhead » Tue Aug 19, 2014 12:43 am

CA_Mouse wrote:
Sqhead wrote:Here is what I use: OG minus FG x .129
Example: Og 1060 - fg 1010 is 50
50x.129 is 6.45 abv


Where did you get 129 from? Most ABV calculators use 131 as the multiplier (including our host's recipe sheets).

(OG - FG) * 131 = %ABV
(1.060 - 1.010) * 131 = 6.55%


You are correct about most calculators using 131. Back when I started brewing there was debate about whether it should be 129 or 131. I went with 129 and stayed with it. No rationale about why since that was many beers ago.
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