Force Carbing Theory Using Weight

If my math's correct

2.5 volumes co2 for 5 gallons beer @ 32f = 12.5 gallons co2 @ 32f
1.5 vol co2 for 5 g beer @ 32f = 7.5 g co2 @ 32f

measurement -> 1cf = 7.480 US gallons OR 1 US Gal = .1336cf
measurement c02 -> 1cf = .1144lb OR 1lb = 8.741 CF

7.5g gallons co2 for 1.5 vol co2 for 5g beer = about 1cf or .1144lb

Ref: 20lb co2 = 174.82cf

Sooo... 12.5 gallons co2 = 2.5 vol co2 for 5g beer @ 32f = 0.1906lb

Btw, I didn't account for head space.

Speaking of head space, if you could properly figure this out you could probably pressurize (given its less than the blow off) all your co2 at once. If you pressurize and weigh the keg instead of the co2 tank, just turn the psi up until you gain the required weight (might be too high for either your tubing or blow off) then rock to equalize or wait. Or hook everything up and tare the keg, put it on desired final co2 rock untill you gain weight.

Oh and to figure out the volume of the beer in your keg you'll have to do some math. It's explained in detail in this PDF from New London Home Brew Club.

http://newlondonbrewclub.com/wp-content/uploads/2014/04/Filling-Kegs-By-Weight-Mike-Branam.pdf

I'd go off of this for your water weights to temperature
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

And water specific gravity to temperature
http://www.engineeringtoolbox.com/water-temperature-specific-gravity-d_1179.html

Don't forget to take into account beer temperature for your FG!

Just adding some more references so that I can compile a better equation (seems he's done most of the work for us) http://www.brainlubeonline.com/GasLawsBeer.html

I'm going to circumvent all your math to tell you that 1 volume is equal to about 2g/L. This is how other countries measure carbonation if I'm not mistaken, so the concept is valid, though I'm not sure the practicality of it for the homebrewer.

5 gallons is about 19L so you're looking for 2.5 x 2 x 19 = 95g That comes out to about 0.2 lbs, so yes your math is correct, even with my rounding.

Let there be zombies!!!

@stamandster i see you're recently seen, so i figured i'd revive your thread, and say i have better luck keeping my co2 tank on the scale while shaking the keg.....and 5 gallons of co2 is 1.23oz's....and then the residule co2 from fermentation is like 1 vol already.....

as far as the practicality of it? i still have to wait 2 days for the kegs to get cold, but at least i don't need to worry about OVER carbing...


here's my very similar thread with helpful calculator, and chart....

https://www.homebrewtalk.com/threads/how-many-ounces-of-co2-for-a-5-gallon-corny.683831/