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?

Simple errors/variations in the programming of those "calculators". Best bet is to take an average of them all.

5.83% ABV

OG-FG and multiply by 131.25.

Weizenwerks said:

OG-FG and multiply by 131.25.

Click to expand...

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.

Weizenwerks said:

OG-FG and multiply by 131.25.

Click to expand...

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.

SumnerH said:

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.

Click to expand...

The simplified formula is good enough for home brewers that want an idea, but don't need much precision.

Weizenwerks said:

The simplified formula is good enough for home brewers that want an idea, but don't need much precision.

Click to expand...

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...

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

You know, after your third beer you're not going to care...

frazier said:

You know, after your third beer you're not going to care...

Click to expand...

I'mnot neerly as think as u drunk i am

Hi folks,
I maintain brewersfriend.com. I updated the ABV calculator there to use the more accurate equation. I'm glad I can improve the tool and serve the brewing community better.

http://www.brewersfriend.com/abv-calculator/

SumnerH said:

Not directed at you: if you're writing brewing software, why use the simple formula? The computer is good at doing math quickly...

Click to expand...

When I originally created the calculator, I ended up coming across the simple formula more often in books I was reading. Since I don't do many high gravity batches, I did not notice how skewed the simple equation gets at the high end of the ABV scale. I learned something from this thread!

Prost!
Larry

larrybrewer said:

Hi folks,
I maintain brewersfriend.com. I updated the ABV calculator there to use the more accurate equation. I'm glad I can improve the tool and serve the brewing community better.

http://www.brewersfriend.com/abv-calculator/



When I originally created the calculator, I ended up coming across the simple formula more often in books I was reading. Since I don't do many high gravity batches, I did not notice how skewed the simple equation gets at the high end of the ABV scale. I learned something from this thread!

Prost!
Larry

Click to expand...

If you don;t mind me asking what equation does your calc use? Is it a simple equation, or is the equation dependent on the difference between the OG and FG?

This might explain why I'm told (as are others) that the beer I make seems stronger than the abv I say it is. Factor in the small boost for priming sugar as well as the less accurate equation, and maybe mine actually are stronger than I've been saying.

muse435 said:

If you don;t mind me asking what equation does your calc use? Is it a simple equation, or is the equation dependent on the difference between the OG and FG?

Click to expand...

His post is saying that it used to use the simple one, but he's just changed it to use the more accurate equation.

larrybrewer said:

Hi folks,
I maintain brewersfriend.com. I updated the ABV calculator there to use the more accurate equation. I'm glad I can improve the tool and serve the brewing community better.

http://www.brewersfriend.com/abv-calculator/



When I originally created the calculator, I ended up coming across the simple formula more often in books I was reading. Since I don't do many high gravity batches, I did not notice how skewed the simple equation gets at the high end of the ABV scale. I learned something from this thread!

Prost!
Larry

Click to expand...

Awesome! Thanks for maintaining the tool, Larry!

I like this one

http://www.rooftopbrew.net/abv.php