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Alcohol By Volume Calculator Updated

Thursday, June 16th, 2011

The Brewer’s Friend ABV Calculator was just updated to include not one, but now two formulas for calculating ABV.  There are two popular formulas out there for calculating ABV.  You can pick the one you prefer for use in your brewing notes.   If you don’t like math, or don’t care that much, just stick with the basic formula. If you are super into math, and want to use the advanced formula (which is supposedly more accurate for high gravity beers), then the alternate equation is now there for you.

Standard Formula:

Most brewing sites use this basic formula:

ABV = (og – fg) * 131.25

This equation was created before the computer age.  It is easy to do by hand, and over time became the accepted formula for home brewers!

Variations on this equation which report within tenths of each other come from The Joy of Homebrewing Method by Charlie Papazian, Bee Lee’s Method, Beer Advocate Method. Some variations use 131 instead of 131.25. The resulting difference is pretty minor.

Alternate Formula:

A more complex equation which attempts to provide greater accuracy at higher gravities is:

ABV =(76.08 * (og-fg) / (1.775-og)) * (fg / 0.794)

The alternate equation reports a higher ABV for higher gravity beers. This equation is just a different take on it. Scientists rarely agree when it comes to equations. There will probably be another equation for ABV down the road.

The complex formula, and variations on it come from Ritchie Products Ltd, (Zymurgy, Summer 1995, vol. 18, no. 2) -Michael L. Hall’s article Brew by the Numbers: Add Up What’s in Your Beer, and Designing Great Beers by Daniels.

 

Why don’t calculators all agree?

  1. The relationship between the change in gravity, and the change in ABV is not linear. All these equations are approximations.
  2. Some calculators round internally as they go. The Brewer’s Friend calculator rounds only at the very end, which means significant digits are kept along the way (making it more true to the equation).
  3. Other online calculators should be close to one of the two equations reported by the Brewer’s Friend ABV Calculator. If not, they are doing their own thing which warrants inquiry.

 

What equation should I use?

Your home brewing friends probably use the basic equation. If you don’t like math, go with the basic equation.

If you are a really tech heavy brewer, and want to brew a lot of high gravity beers, or prefer Daniels over Papazian, use the advanced equation.

Either way, they are close for beers below 6% ABV.   The difference does get larger as the gravity increases.   For a brew with OG 1.092, and an FG of 1.021, the standard equation reports an ABV of 9.32%, while the alternate equation reports 10.17%, that’s a difference of 0.85%.  At that alcohol level, after a few beers, maybe it doesn’t matter so much… hehe ;)

Prost!

Legal Disclaimer: The Brewer’s Friend ABV calculator is for entertainment purposes and should not be used for professional brewing. No warranty or guarantee of accuracy is provided on the information provided by this calculator.

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