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Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Calculating ABV
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Old 02-17-2011, 06:01 AM   #1
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Default Calculating ABV

So i have BeerAlchemy on my mac and a trial of Beer Smith on my PC. When i entered my last batch in to BS i got a different ABV than with BA. I tried a couple of online calculators and got some more ABVs

5.9 - rooftopbrew.net
5.78 - brewersfriend.com
5.74 - Beer Smith
5.9 - BeerAlchemy

Why am I getting a variety of different ABVs?

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Old 02-17-2011, 06:36 AM   #2
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Simple errors/variations in the programming of those "calculators". Best bet is to take an average of them all.

5.83% ABV

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Old 02-17-2011, 06:45 AM   #3
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OG-FG and multiply by 131.25.

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Old 02-17-2011, 01:14 PM   #4
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Quote:
Originally Posted by Weizenwerks View Post
OG-FG and multiply by 131.25.
That's the simplified but less accurate formula; it underestimates slightly in the <7% ABV range and underestimates more significantly for bigger beers.

More accurate:
abw=76.08*(og-fg)/(1.775-og)
abv=abw*(fg/.794)


The Brewer's Friend site is using the simplified algorithm.

Rooftopbrew looks to be using the more accurate one (BeerAlchemy has the same answer so is presumably using the same algorithm).

BeerSmith must be using the simplified one and rounding things off too early in the process or something.
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Old 02-17-2011, 01:20 PM   #5
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Quote:
Originally Posted by Weizenwerks View Post
OG-FG and multiply by 131.25.
I'll have to remember this. Of course factoring for temp too. I adjusted my og by 1 point and my abv went from 7.87 to 8.0.
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Old 02-17-2011, 03:40 PM   #6
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Quote:
Originally Posted by SumnerH View Post
That's the simplified but less accurate formula; it underestimates slightly in the <7% ABV range and underestimates more significantly for bigger beers.

More accurate:
abw=76.08*(og-fg)/(1.775-og)
abv=abw*(fg/.794)


The Brewer's Friend site is using the simplified algorithm.

Rooftopbrew looks to be using the more accurate one (BeerAlchemy has the same answer so is presumably using the same algorithm).

BeerSmith must be using the simplified one and rounding things off too early in the process or something.
The simplified formula is good enough for home brewers that want an idea, but don't need much precision.
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Old 02-17-2011, 05:38 PM   #7
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Originally Posted by Weizenwerks View Post
The simplified formula is good enough for home brewers that want an idea, but don't need much precision.
Yep, but the poster was asking why different software was giving him different numbers. The answer is that 2 of them are using the more precise formula, one's using the simple formula, and one's doing something weird.

Not directed at you: if you're writing brewing software, why use the simple formula? The computer is good at doing math quickly...
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Old 02-17-2011, 06:05 PM   #8
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After doing some more looking online i found that different require different formulas, I assume the reason why i kept getting different results is due to the fact that programmers are lazy and only wrote a single line of code for the calculations. I'm guessing that they used a medium value for F that will/should give a good approximation, with higher degrees of inaccuracy at the extremes.

As a result i'm now writing my own code based on the UK customs office definition of ABV. I'm not sure if it will be right but hey, its something to do at work

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Old 02-17-2011, 07:08 PM   #9
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You know, after your third beer you're not going to care...

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Old 02-17-2011, 07:29 PM   #10
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Quote:
Originally Posted by frazier View Post
You know, after your third beer you're not going to care...
I'mnot neerly as think as u drunk i am
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