Author Topic: ABV calculator based on volume?  (Read 384 times)

Offline KCguy

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ABV calculator based on volume?
« on: August 24, 2019, 12:51:57 PM »
Maybe the guys who do 10 or more gallons will comment here, but I need an ABV calculator that will let me change the volume, instead of assuming the standard 5 gallons.  Ive had more than a few batches that ended up with almost 6 gallons by bottling time and I need a more accurate way to calculating that abv.  All the online cals seem to simply assume 5g, and Im not seeing a way to edit that volume.
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Offline jverduin

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Re: ABV calculator based on volume?
« Reply #1 on: August 24, 2019, 02:30:00 PM »
I thought abv calculations are a simple function of change in gravity. I didn’t think volume of beer had a place in the calculation.

Most calculators use:
ABV = (OG - FG) * 131.25




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Offline a10t2

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Re: ABV calculator based on volume?
« Reply #2 on: August 24, 2019, 02:46:48 PM »
Right, any ABV calculation based on gravity readings is by definition an estimate, but volume doesn't factor into either an estimate or a real ABV measurement.
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Offline KCguy

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Re: ABV calculator based on volume?
« Reply #3 on: August 24, 2019, 03:36:00 PM »
Wait a minute - Isnt ABV = Alcohol by VOLUME?  And wouldnt more volume decrease the amount of alcohol present in each glassful/sip?   

I mean, if I have 5%abv in a 5 gallon batch, then I added 1g water to it, wouldnt that decrease the alcohol overall? 
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Offline stpug

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Re: ABV calculator based on volume?
« Reply #4 on: August 24, 2019, 03:43:42 PM »
Wait a minute - Isnt ABV = Alcohol by VOLUME?  And wouldnt more volume decrease the amount of alcohol present in each glassful/sip?   

I mean, if I have 5%abv in a 5 gallon batch, then I added 1g water to it, wouldnt that decrease the alcohol overall?

If you're talking about dilution (or concentration - assuming no alcohol losses) then that would be:
(Original_Volume*Original_ABV)/New_Volume = New_ABV

But, like the other folks said, no volumes are needed for ABV calculations based on gravities.

Offline Kevin

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Re: ABV calculator based on volume?
« Reply #5 on: August 24, 2019, 10:04:49 PM »
It's the OG and FG of your batch that gives you the ABV of any particular size batch of beer.
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Offline tommymorris

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Re: ABV calculator based on volume?
« Reply #6 on: August 24, 2019, 11:21:31 PM »
The OP’s confusion is certainly understandable based on the expanded acronym.

From Wiki:

ABV is defined as the number of millilitres (mL) of pure ethanol present in 100 mL (3.4 fl. oz) of solution at 20 °C (68 °F).

*The volumes are constant.


Offline jverduin

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Re: ABV calculator based on volume?
« Reply #7 on: August 24, 2019, 11:37:58 PM »
Wait a minute - Isnt ABV = Alcohol by VOLUME?  And wouldnt more volume decrease the amount of alcohol present in each glassful/sip?   

I mean, if I have 5%abv in a 5 gallon batch, then I added 1g water to it, wouldnt that decrease the alcohol overall?
Yes... adding a 1g of water to it would decrease the alcohol. You’d need to recalc the starting OG downward and the FG downward.

But if you are measuring ABV... the size of the batch of beer is not relevant to the calculation.


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Offline Bob357

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Re: ABV calculator based on volume?
« Reply #8 on: August 25, 2019, 03:11:12 AM »
ABV = 5.2% means that the alcohol is 5.2% of the volume. The volume isn't part of the equation and is irrelevant. 5% of 5 gallons is the same percentage as 5% of 10,000 gallons. Capiche?
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Online Robert

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Re: ABV calculator based on volume?
« Reply #9 on: August 25, 2019, 03:24:42 AM »
ABV = 5.2% means that the alcohol is 5.2% of the volume. The volume isn't part of the equation and is irrelevant. 5% of 5 gallons is the same percentage as 5% of 10,000 gallons. Capiche?
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Offline jverduin

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Re: ABV calculator based on volume?
« Reply #10 on: August 25, 2019, 02:13:19 PM »
Wait a minute - Isnt ABV = Alcohol by VOLUME?  And wouldnt more volume decrease the amount of alcohol present in each glassful/sip?   

I mean, if I have 5%abv in a 5 gallon batch, then I added 1g water to it, wouldnt that decrease the alcohol overall?

Maybe a helpful way to look at it: If you had a pint glass of beer and poured 12 ozs of 5% abv beer into it - and then filled the rest with 4 ozs of water - you would definitely reduce the ABV overall. But, if you poured 4 more ozs. of the same 5% ABV beer into the glass instead of water, the ABV will still be 5% ABV. Your volume went up in both cases, but the water made the ABV go down in the first example because water is 0% ABV.

Offline KCguy

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Re: ABV calculator based on volume?
« Reply #11 on: August 25, 2019, 05:00:32 PM »
ABV = 5.2% means that the alcohol is 5.2% of the volume. The volume isn't part of the equation and is irrelevant. 5% of 5 gallons is the same percentage as 5% of 10,000 gallons. Capiche?

OK, gotcha.  That makes sense. 
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Michael B
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Offline KCguy

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Re: ABV calculator based on volume?
« Reply #12 on: August 25, 2019, 05:01:39 PM »
Yes... adding a 1g of water to it would decrease the alcohol. You’d need to recalc the starting OG downward and the FG downward.

But if you are measuring ABV... the size of the batch of beer is not relevant to the calculation.

So, HOW do I recalc the FG and OG downward as you say?  I guess thats my question from the start...
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Michael B
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Offline Visor

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Re: ABV calculator based on volume?
« Reply #13 on: August 25, 2019, 05:33:45 PM »
   One easy way is to multiply the OG by the gallons of wort/beer and divide by the number of gallons of diluted wort/beer. For example 5 G of 1.065 wort diluted with 1 G of H2O would be 65x5=325 gravity points divided by 6G = 54 or 1.054. Measure the FG after dilution and calculate your ABV from the adjusted OG [1.054]. Hope that didn't muddy the water.
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Offline KCguy

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Re: ABV calculator based on volume?
« Reply #14 on: August 25, 2019, 06:00:42 PM »
   One easy way is to multiply the OG by the gallons of wort/beer and divide by the number of gallons of diluted wort/beer. For example 5 G of 1.065 wort diluted with 1 G of H2O would be 65x5=325 gravity points divided by 6G = 54 or 1.054. Measure the FG after dilution and calculate your ABV from the adjusted OG [1.054]. Hope that didn't muddy the water.

Not muddy, I understand that.  But I didnt actually add water to the beer/wort, not sure if I should recalc or not?  Its just that I ended up with 6 gallons because I started with 8g of RO water at mash in, which ended up at 5.75g post boil vol, and just before bottling I added a 2000ml starter (for reyeasting/bottle conditioning) which made the whole volume just a tad under 6gallons. 

If I recalc as above, for 6 gallons, then my abv drops from 10.5% (OG1.086, FG1.006)  to 7.8%.  Which is the truer abv? 
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Michael B
Kansas City