Homebrewers Association  AHA Forum
General Category => Equipment and Software => Topic started by: 69franx on May 14, 2015, 08:52:24 PM

So some googling tells me the volume surrounded by a cylinder = pi*r^{2}*H. When I plug manufacturer's specs for my kettle into this equation, I get roughly 3.14*64*19.2 from the formula here: http://www.smartconversion.com/unit_calculation/Volume_of_a_Cylinder.aspx (http://www.smartconversion.com/unit_calculation/Volume_of_a_Cylinder.aspx)
and this says it equals 16.7gallons in my kettle. My main issue is that when I measure the interior dimensions of the kettle, I get a radius of 7.25" and total height of let's call it 18 7/8". Plugging these measurements into the formula yields a volume of just under 13.5 gallons. This kettle was marketed through kickstarter as a 15 gallon kettle, so I am wondering if my math is off somewhere. I have weighed water by the gallon (8.35#/gallon) as I have filled the kettle with strike water and the volume never matches the manufacturer's etchings on the inside. My measurements were made with what I take to be an accurate tape measure. the reason this all matters is that this weekend, I have my first 10 gallon batch planned that will require 12.5 boil volume or adjust with top off water. If I actually have the 16.7 gallons, I am not concerned, but if I only have roughly 13.514 gallons inside, I am very concerned. can anyone help me trouble shoot the math to ease my mind? I know Mark had a formula posted in a thread somewhere that would help me here, but it was not specifically a kettle volume thread, so I'm having trouble narrowing down search results. Very long winded I know, but can anyone help me?

So some googling tells me the volume surrounded by a cylinder = pi*r^{2}*H. When I plug manufacturer's specs for my kettle into this equation, I get roughly 3.14*64*19.2 from the formula here: http://www.smartconversion.com/unit_calculation/Volume_of_a_Cylinder.aspx (http://www.smartconversion.com/unit_calculation/Volume_of_a_Cylinder.aspx)
and this says it equals 16.7gallons in my kettle. My main issue is that when I measure the interior dimensions of the kettle, I get a radius of 7.25" and total height of let's call it 18 7/8". Plugging these measurements into the formula yields a volume of just under 13.5 gallons. This kettle was marketed through kickstarter as a 15 gallon kettle, so I am wondering if my math is off somewhere. I have weighed water by the gallon (8.35#/gallon) as I have filled the kettle with strike water and the volume never matches the manufacturer's etchings on the inside. My measurements were made with what I take to be an accurate tape measure. the reason this all matters is that this weekend, I have my first 10 gallon batch planned that will require 12.5 boil volume or adjust with top off water. If I actually have the 16.7 gallons, I am not concerned, but if I only have roughly 13.514 gallons inside, I am very concerned. can anyone help me trouble shoot the math to ease my mind? I know Mark had a formula posted in a thread somewhere that would help me here, but it was not specifically a kettle volume thread, so I'm having trouble narrowing down search results. Very long winded I know, but can anyone help me?
The radius is 7.25" (14.5" divided by two)
The radius squared is 7.25" X 7.25" which equals 52.56
So now we have 3.14 X 52.65 X 18.875 (height) = 3120 (this is the total cubic inches in the pot)
3120 / 231 = 13.5 (the number of gallons the pot will hold)
your math seems correct if your measurements are correct.

Thanks ken,
now I'm pissed at the manufacturer again
Now that I see you run the math, I realize I'm the dumb#$%. Half of my diameter is 7.75, not 7.25. And to think I think of myself as a math guy! Plugging that into the formula gives me a volume of roughly 15.42 gallons, so its as advertised. Think with a little ferm cap I will still be good to go as long as I keep a watchful eye on it. Thanks again.

Thanks ken, now I'm pissed at the manufacturer again
Now that I see you run the math, I realize I'm the dumb#$%. Half of my diameter is 7.75, not 7.25. And to think I think of myself as a math guy! Plugging that into the formula gives me a volume of roughly 15.42 gallons, so its as advertised. Think with a little ferm cap I will still be good to go as long as I keep a watchful eye on it. Thanks again.
Haha! It happens. Glad you figured it out and can breathe now Frank.
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