OG -> FG = ABV Math

I know if I actually surfed I could find it. If you understood What I did for work and had the day I did you would do the same thing. I DO SEARCH. Just not tonight


What is the Math equation you all use to calculate OG from FG to give you your ABV?


Thanks all for not giving me any heat over this. I am just tired

Og - Fg * 131

Chimone said:

Og - Fg * 131

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Dont think that is right

here is what I get

OG is 1041
FG is 1001

then if I multiply by 131 I get 5,240 so ABV is 5.24? is that correct?

sAvAgE said:

Dont think that is right

here is what I get

OG is 1041
FG is 1001

then if I multiply by 131 I get 5,240 so ABV is 5.24? is that correct?

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That's exactly right. You just need to remember where the decimal goes:

1.041 - 1.001 = 0.040
0.040 * 131 = 5.24%

Yuri_Rage said:

That's exactly right. You just need to remember where the decimal goes:

1.041 - 1.001 = 0.040
0.040 * 131 = 5.24%

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OK Great thanks Guys. Cheers to you all

Funny, TCJOHB, 3rd ed, page 43 says:

OG - FG * 105 = ABW

ABW * 1.25 = ABV

homebrewer_99 said:

Funny, TCJOHB, 3rd ed, page 43 says:

OG - FG * 105 = ABW

ABW * 1.25 = ABV

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Funny...

105 * 1.25 = 131.25.

You're just "showing your work."

Yuri_Rage said:

Funny...

105 * 1.25 = 131.25. You're just "showing your work."

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OK, you're missing it...

Let's say:

OG = 1.055
FG = 1.012
difference = .043

.043 * 105 = 4.515% ABW

4.515 * 1.25 = 5.64% ABV

No...you're adding a step to a simple calculation (unless I'm missing a joke here...).

The formula you're using can be simplified to:
((OG - FG) * 105) * 1.25 = ABV

Therefore:
(OG - FG) * 131.25 = ABV

So:
0.043 * 131.25 = 5.64% ABV

Yuri_Rage said:

No...you're adding a step to a simple calculation (unless I'm missing a joke here...).

The formula you're using can be simplified to:
((OG - FG) * 105) * 1.25 = ABV

Therefore:
(OG - FG) * 131.25 = ABV

So:
0.043 * 131.25 = 5.64% ABV

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I think the only step I'm adding is the one to get ABW.

homebrewer_99 said:

I think the only step I'm adding is the one to get ABW.

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Right, but the OP asked for ABV, so calculating ABW is unnecessary and can be combined into a single equation for ABV (see associative property for multiplication in a basic algebra book).

Not trying to be an ass, just trying to explain that your method achieves EXACTLY the same result with more work.

Og - Fg * 131

Chimone said:

Og - Fg * 131

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Well, since this thread seems to have turned into an algebra lecture, it's technically:

(Og - Fg) * 131

Yuri_Rage said:

Right, but the OP asked for ABV, so calculating ABW is unnecessary and can be combined into a single equation for ABV (see associative property for multiplication in a basic algebra book).

Not trying to be an ass, just trying to explain that your method achieves EXACTLY the same result with more work.

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True, true. You weren't being an ass as far as I am concerned...

I realize what the problem (me was...).

I was only placing both ways there in case someone wants to know how to calculate both %.

Guys, since my hydrometer has the potential alcohol scale on it, you can just look at a hydrometer, and read it.

Find your OG mark, on the SG scale. Find the initial potential alcohol mark that corresponds with your OG. Find the same pot. EToH for FG, and subtract the smaller, from the larger. Just use the hydrometer as a scale.

steve

wow I just devide the differance by 75
cheers

This thread turned out very informative. What a way to have fun and get it all out and fully explained Thanks Guys *CHeers

Here is a site on beer math


Beer Math

LS_Grimmy said:

Here is a site on beer math


Beer Math

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Great Site Man!!! It is now bookmarked!

sAvAgE said:

Great Site Man!!! It is now bookmarked!

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Glad you liked it... enjoy

Yuri_Rage has got it right...

or for more completeness:

og - fg * 131.25

yes, that .01% ethanol does matter!

I hope it isn't too late to jump in on this math discussion.
Dr. Michael Hall, in his article entitled "Brew by the Numbers - Add up What's in Your Beer" (Zymurgy, summer 1995), has an equation that takes into consideration, the presence of the ethanol in the ABV debate:

ABV = ABW * (FG / 0.794), where 0.794 is the SG of ethanol.

And ABW as this:

ABW as: ABW = 76.08 * (OG – FG) / (1.775 – OG)

So if OG is Original Gravity of 1.055,
and FG is Final Gravity of 1.012,

ABW = 76.08 * (OG – FG) / (1.775 – OG)
ABW = 76.08 * (0.043) / (0.72)
ABW = 4.54

ABV = ABW * (FG / 0.794)
ABV = 4.54 * (1.27)
ABV = 5.78%

The .pdf in link has all the accurate equations for beer makers (Mead maker myself) and their process' like extract values, attenuation coefficient, etc...

DV8DUG said:

I hope it isn't too late to jump in on this math discussion.

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Well, you are adding to a thread that is 7 years old.

The simplest one is ABV = OG.

For example, if the OG is 1.055, the ABV is 5.5. If the OG is 1.040, the ABV is 4.0.

That only works if you assume about 76% attenuation by the yeast, but that's a decent assumption for me and most of the beers I brew.

passedpawn said:

The simplest one is ABV = OG.

For example, if the OG is 1.055, the ABV is 5.5. If the OG is 1.040, the ABV is 4.0.

That only works if you assume about 76% attenuation by the yeast, but that's a decent assumption for me and most of the beers I brew.

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Ummm.... NO

DV8DUG said:

Ummm.... NO

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Which part do you disagree with?

@day_trippr Your post made me laugh!

allanmorgan said:

@day_trippr Your post made me laugh!

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me too!

I know it is old, but I have in the short time that I have been brewing just took the difference in the last three digits divide by 7.62

ie

1.050 OG
1.010 FG

Diff = 40
/7.62
= 5.25% ABV

For my own edification, does anyone know the cutoff in gravity which one would use the "alternate" calculation method as selectable on the Brewer's Friend calculator (outlined by @DV8DUG above)?

Thanks!