# Alcohol % by volume question

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#### Mesa512

##### Well-Known Member
Hey guys,

I was going to have labels made for my first batch of beer. On there I would like to include the % alcohol by volume. Is there a way to calculate it for a homebrew? If so can you explain how I would do it. Thank you

(fg-og) * 131

#### EoinMag

##### Well-Known Member
arcanexor, you're assuming an awful lot with your mathematical answer there, if the guy doesn't know that you can calculate % alc, what are the chances he'll know what fg and og stand for?

#### SumnerH

##### Well-Known Member
arcanexor, you're assuming an awful lot with your mathematical answer there, if the guy doesn't know that you can calculate % alc, what are the chances he'll know what fg and og stand for?

Well, if he measured them he'll know what they are.

And if he didn't, there's no way he'll be able to calculate ABV; he'll need a spectrometer or something to measure it directly.

#### Parker36

##### Well-Known Member
Hey guys,

I was going to have labels made for my first batch of beer. On there I would like to include the % alcohol by volume. Is there a way to calculate it for a homebrew? If so can you explain how I would do it. Thank you

How to Brew - By John Palmer - Introduction

#### Stef1966

##### Well-Known Member
Man...
Just run to your LHBS and buy a Hydrometer, that little glass thing will able you to take readings and calculate the gravity of your beer while in process and use the given formula to predict quite accurately, the % of Alcohol per volume you can expect from your beer batch.

(OG - FG) X 131 = ABV
OG= "Original Gravity" i.e the initial Hydrometer reading before pitching the yeast.
FG= "Final Gravity" i.e the last reading you will take and then decide it's probably time to bottle or keg it all up.

Also, SG meaning "Specific Gravity" would be any reading you would take during fermentation process to witness to occuring of the fermentation process in course of action.

Im answering this here, but all the guys above could have, they probably are just too fed up with answering this thing over and over again now...

#### alee

##### Well-Known Member
you guys have a strange way of welcomming a new guy to brewing!
At least he is getting his feet wet.

#### ssabin

##### Well-Known Member
This is the formula I use, have found elsewhere on the net, and seems to be what the calculator on Rooftopbrew.net uses - at least a few folks are using it:

Alcohol percentage by weight equals 76.08 times Original Gravity minus Final Gravity divided by 1.775 minus Original Gravity. It is easier to scribble this down: ABW = 76.08(OG-FG)/(1.775-OG).

You should remember that ABW is used mostly in the United States, while the rest of the beer world (as well as the wine and spirits world) measures Alcohol by Volume (ABV). That conversion is easy: ABV = ABW (FG/.794).

The simplified formula (OG-FG)*131 gives a slightly different answer. However, do note that even if the first, more complex formula is considered "better", even that formula is still an estimate of your ABV. Since few, if any of us, have the means to actually measure the alcohol in a more scientific manner, we use these calculations as a good approximation to the ABV and call it done. These approximations assume that 100% of the change in SP is due to fermentables being converted to alcohol. This is accurate enough in most cases, but isn't necessarily always a good explanation for what happened to your particular wort!

#### llazy_llama

##### Well-Known Member
you guys have a strange way of welcomming a new guy to brewing!
At least he is getting his feet wet.

It's not that we're hard on him because he's new, we're hard on him because he hasn't made even the slightest effort to figure something out on his own before he asked the question here. Even a quick search on this forum or a google search on "how to calculate ABV in homebrew," would have answered the question.

It's not the end of the world, or anything worth stressing out over, but it happens every day. We're just doing our part to keep the redundant threads to a minimum, not trying to flame the poor guy.

#### mahilly

##### Well-Known Member
The simplified formula (OG-FG)*131 gives a slightly different answer. However, do note that even if the first, more complex formula is considered "better", even that formula is still an estimate of your ABV. Since few, if any of us, have the means to actually measure the alcohol in a more scientific manner, we use these calculations as a good approximation to the ABV and call it done.

My hydrometer has three scales: "SG", "Potential ABV" (plus one other I don't use). On the potential ABV scale I just subtract the final reading from the original reading to determine "actual" ABV. I read somewhere that this wasn't good practice, but that is exactly what the instructions on the hydrometer say to do. This also yields the exact same result as (OG-FG)*131 (I checked). So I'm not sure why this is a problem. I'm sure someone here will enlighten me though.

OP
OP
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#### Mesa512

##### Well-Known Member
just so you guys know I did do some research. I didn't understand the terminology they were using to explain it, so I figured I would come here next. I understand though how annoying it is to have the same threads everyday. No hard feelings. cheers

#### fretsforlife

##### Well-Known Member
Before I even knew what a hydrometer was, I watched this quick video. It takes pretty much all the guesswork out of it, and the guy who made it really cracks me up. definitely check this out..

#### ChshreCat

##### Well-Known Member
just so you guys know I did do some research. I didn't understand the terminology they were using to explain it, so I figured I would come here next. I understand though how annoying it is to have the same threads everyday. No hard feelings. cheers

Best advise then is to go to that link for How To Brew and read up. That'll give you pretty much everything you need to understand anything on here. It really is an excellent place to start learning about homebrewing.

#### BarleyWater

##### Well-Known Member
just so you guys know I did do some research. I didn't understand the terminology they were using to explain it, so I figured I would come here next. I understand though how annoying it is to have the same threads everyday. No hard feelings. cheers

We could make a fairly educated guess on what it would be if you just post your recipe. If it was mainly extract, then it is unlikely that there would be much swing in the calculation you get when formulating a recipe, so no OG and FG needed, although they would make it more accurate.

So just post the recipe and it should be easy to figure out about what the numbers are, and then go read How to Brew, www.howtobrew.com, it's an invaluable resource to beginning homebrewers.

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