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Help with some beer math

Hey guys,

In my head I figured I could do this math, but every single method I tried yielded clearly incorrect results. Here’s what I’m looking for.

I just brewed up a batch and had a measured OG of 1.070, however I also ended up with about 4.5 gallons of wort instead of the 5 I was shooting for. I was way over on my efficiency estimate though, so I figured I would just top it off to the 5.0 gal mark. This was I have a bit more beer, and it will bring down the gravity more into the range I was shooting for anyway. However, no matter what way I tried to work the math (and I tried 2 or 3 ways) I kept getting clearly incorrect results. Apparently I either don’t remember how to do my weighted averages or that math wont work here.

At any rate, can someone share the correct formula for figuring out the new OG with the extra half gallon of water added?

Thanks fellas,

subtract the new sample from old sample. bing!


If you diluted 4.5 gallons of wort at 1.070 to 5 gallons the resulting gravity will be 1.063.

Adding water calculation (metric):

Present volume * current gravity = extract
Extract/ desired gravity = needed volume
Needed volume - present volume= water that needs to be added

Here comes the algebra. (5 gallons = 18.9 liters) and (4.5 gallons = 17 liters)

17 liters * 70 gravity = 1190 extract

1190 extract / X = 18.9 liters

1190/18.9= 62.96 gravity


So your gravity is about 1.063

I must be lazy, I like it when people develop calculators for this. :slight_smile:

you guys & your fancy math. tell me, fancy pants’s, how many average Belgian Tripels do you need to consume to repel zombies? assuming you haven’t had any Belgian styles 3 months prior, of course. :cheers:

Assuming each Belgian is about 8.5% abv. And my liver processes 1 drink an hour. I’d say I would need 4 Belgian tripels consumed in 1 hour for 3 hours of zombie resistance

Not to repel zombies, just to stumble around and fit in with the hoard :wink:

I’m just gonna keep drinkn’ till those zombie ladies start lookn’ good! That’s after I brew my Belgian triple of course.

After sleeping on it a night I remembered my error, and my new results match yours! Thanks much fellas!

[quote=“Trimack”]After sleeping on it a night I remembered my error, and my new results match yours![/quote]I’d guess that you were trying to use 1.070 rather than 70 to do the math… :wink:

Yes and no. I was using 1.07 to do the math, but I was forgetting that the half gallon of water still had a gravity reading of 1.00 and not 0.00. So yes, but it will work either way (so long I remember my silly weighted averages!)

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