# Gravity calculation

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#### pwndabear

##### Well-Known Member
Just brewed a partial mash smoked porter tonight (recipe at bottom):

So I took my OG and it read 1.058 where my target was 1.049. I realized after I had put it into my carboy that I was a half gallon short.

I topped off with a half gallon and added 800ml of starter (which was simply 2oz of DME with two cups of water and topped up to 800ml with 1 pack of yeast added that was sitting for a day).

Does anyone know what my actual OG is going to be? I was unable to take a sample from the carboy and figured that a calculation would be able to determine the OG value... I wouldn't imagine it would be too far off, maybe 1.054 or so but if someone can answer this and show how they got their conclusion (remember math class kiddies?), I would be more than appreciative.

5.00 lb Smoked Malt (9.0 SRM)
3.00 lb Munich LME - 10L (10.0 SRM) (60 min)
0.25 lb Black Patent (2.0 SRM)
0.50 lb Caramel/Crystal Malt - 60L (40.0 SRM)
0.50 lb Chocolate Malt (250.0 SRM)

0.50 oz Northern Brewer [8.50%] (60 min)
1.00 oz Williamette [5.20%] (60 min)
0.50 oz Northern Brewer [8.50%] (20 min)
1 tsp Irish Moss (15 min)

Wyeast London Ale 1028

#### MalFet

##### /b&#618;&#601;r n&#604;rd/
Easy as pie!
(volume A) * (gravity A) = (volume B) * (gravity B)

#### Yooper

##### Ale's What Cures You!
Staff member
Mod
Well, if you had 4.5 gallons of 1.058 wort, and added a half gallon of water, that would be 1.052.

Then, you added .85 quarts of 3% beer. That shouldn't affect it much at all.

Let's see, 5 gallons at 1.052 pus .85 quarts of 3% beer. When I'm not into a few beers, I can finish the rest!

OP

#### pwndabear

##### Well-Known Member
man my head hurts trying to figure this one out. i hate math.

#### wailingguitar

##### Well-Known Member

Beer will be good, smile and enjoy

#### MalFet

##### /b&#618;&#601;r n&#604;rd/
man my head hurts trying to figure this one out. i hate math.
4.5 gal * 58 = 5 gal * ???

From there, you added 800mL of water and 2oz of DME:

5 gal + 800mL = 5.21 gallons

thus:
4.5 gal * 58 = 5.21 gal * ???

or, 1.050 gravity.

DME contributes on average 44 points per pound per gallon, and you added 0.125 lb into 5.21 gallons, so:

44 * 0.125 / 5.21 = about 1.

So, your hypothetical pre-fermentation gravity (as if you had just mixed all this stuff together at the same time) was near 1.051. Your actual pitching gravity can't really be determined, since it would depend on how much of your starter got eaten up by the yeast in the 24 hours since you built it, but it will be somewhere between 1.050 and 1.051

OP

#### pwndabear

##### Well-Known Member
damnit i dont know if this makes a difference at all in the calculations but the volume was supposed to be 5.5 and i had 5gallons. i topped up to 5.5... is it all relative?

lets see

5.0 * 58 = 5.5 * x

hpw did you figure that adding a half gallon of water brought the grav down to that specific point?

5.5 gal + 800ml = 5.71 gal

im not following the actual math here

#### MalFet

##### /b&#618;&#601;r n&#604;rd/

5 gallons of wort at 1.058

which is (5*58=290) 290 points of gravity.

Divide that by your new gravity (290 / 5.5 = 52.7) to get 1.053

OP

#### pwndabear

##### Well-Known Member
OOOOOOHO I get it now. thanks man! I appreciate it and then some!

I posted pics of the brewday on Facebook. If anyone is interested, you can become a fan of Rochester Suds to take a look!