# Online Alcohol Calculators



## entilza (16/12/08)

Hi gang,

Has anyone else noticed a WILD variation in the results from online alcohol calculators? Using an original SG of 1042 (42), and a finishing SG of 1002 (02), we get some pretty wild and wooly results. 

eg

http://www.brewcraft.com.au/wa.asp?idWebPa...p;idDetails=117
Result: 6.1%

http://www.homebrew.com.sg/alcohol_calculator.htm
Result: 5.847%

http://kotmf.com/tools/alcohol.php
Result: 5.2%

Can anyone recommend an online calculator that they KNOW is OK?

Cheers,
Jason (entilza)


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## quantocks (17/12/08)

I use this one > http://www.homebrew.com.au/wa.asp?idWebPag...p;idDetails=172

but like you said, they're very rarely accurate and should only be used as a guide.


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## Millet Man (17/12/08)

Entilza said:


> Hi gang,
> 
> Has anyone else noticed a WILD variation in the results from online alcohol calculators? Using an original SG of 1042 (42), and a finishing SG of 1002 (02), we get some pretty wild and wooly results.
> 
> ...


Promash give 5.25% for that OG/FG so I'd say the last one on your list is the right one to use.

Cheers, Andrew.


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## Hashie (17/12/08)

Beer Smith gives 5.21%, so I agree with Millet Man, go with the last one.


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## Fermented (17/12/08)

Why not do it by hand?

ABV% = (OF-FG)/7.46

Add 0.5% to the result if bottle conditioning.

NB: I don't remember where 7.46 came from. I suspect it was from one of the Coopers Kit instruction sheets.

Cheers - Fermented.


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## entilza (17/12/08)

Hi team,

Great responses there. Thanks very much for the insight. And I never knew the calculation could be so easy - I saw somewhere a rather complex calculation, so I guess that 7.46 is an approximation of sorts. But still, it implies the lower figure is the correct one.

Ta!
Jason (Entilza)


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## randyrob (17/12/08)

i get 5.2% using

(og-fg) * 0.13

1042-1002 = 40

40 * 0.13 = 5.2%


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## jonocarroll (17/12/08)

You want to get it right? Ask a physicist... The chemistry of it isn't too hard to follow;

Reaction: C[size=-1]6[/size]H[size=-1]12[/size]O[size=-1]6[/size] => 2(CH[size=-1]3[/size]CH[size=-1]2[/size]OH) + 2(CO[size=-1]2[/size]) (assuming you are breaking down glucose - this is an *assumption* and the results will depend on it.

So for every glucose molecule you get 2 ethyl alcohol and 2 carbon dioxide molecules.

molecular_weight_ethyl_alcohol = 46.0688 g/mol
molecular_weight_carbon_dioxide = 44.0098 g/mol

So for every gram of CO[size=-1]2[/size] that leaves the reaction, you get 1.047 grams of ethyl_alcohol.

The difference in SG is due to the loss of CO[size=-1]2[/size] so we want (OG-FG) = 1.042 - 1.002 = 0.040. This is the g/L of CO[size=-1]2[/size] that escapes.

The weight of ethyl_alcohol is then 1.047 x ( OG - FG ) = 0.0419 g/L = 4.2% alcohol by weight.

density_water = 0.998 kg/L (@ 20*C)
density_ethyl_alcohol = 0.789 kg/L (@20*C)

Since ethyl_alcohol is less dense, we use the density to calculate the alcohol by volume and get

4.19% / 0.789 = 5.308% alcohol by volume.

The other calculations people have used are the short-cuts to this. All up you need

( OG - FG ) * 1.047 / 0.789 = ABV

Notice that:

[*] 1.047 / 0.789 = 1.327, hence randyrob's calc.
[*] 1 / ( 1.047 / 0.789 ) = 0.756, hence Fermented's calc

Factors of 10 and 100 sneak in to these if you use 40 points instead of 1.040, or you magically get a percentage from dividing two numbers. Differences arise by not just assuming all the sugars are glucose, and by adding 0.5% randomly for carbonation.

CHEERS! :icon_cheers:


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## joecast (17/12/08)

QuantumBrewer said:


> You want to get it right? Ask a physicist... The chemistry of it isn't too hard to follow;


love it! you've been a busy boy lately QB. thanks
joe


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## 2much2spend (20/5/12)

http://www.brewing-tips.com/abv-alcohol-calculator/

:chug:


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## QldKev (20/5/12)

Entilza said:


> Hi gang,
> 
> Has anyone else noticed a WILD variation in the results from online alcohol calculators? Using an original SG of 1042 (42), and a finishing SG of 1002 (02), we get some pretty wild and wooly results.
> 
> ...




As already mentioned Brewcraft is over estimating it, the second 2 both look good. 

From the second link:_ "Note: The calculated alcohol percentage includes the addition of priming sugar used for bottle conditioning"_


QldKev


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## bignath (20/5/12)

Havent looked at any of those limks but:

I wouldnt believe anything that comes from a brewcraft website or store.

Out of the other two options...it looks like one is taking into account bottle conditioning which loosely adds another .5%ABV.


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## 2much2spend (20/5/12)

yeah i couldnt make sense of the BC calc so i came across another one i like it
so thought i would post it in case anyone else was searching. :icon_cheers:


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## TasBrewBQ (21/10/12)

May be no help but I just tried this one:

http://flavoursomedelights.com/Beer/Tips/alccalc.html 

It appears to take the ambient temp into account but I was actually looking for one I have lost the bbokmark for that factors in yeast attenuation rates as the alcohol levels get higher. 

There was a website i used to use a lot that said it used the same algoritim as UK Customs and Excise use to calculate tax.
I figured that the Poms have been making and taxing beer for a fair while so may have it close to accurate????

If any one finds that one a post here would be grand.


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