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 Home Brew Forums > Making a Volume Measuring Stick

11-12-2011, 02:48 AM   #1
Rcole
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 Making a Volume Measuring Stick

Hi,

I'm sure this formula is on the boards here somewhere, but thought I would post the formula for marking a stick to measure the volume of liquid in a round container as a function of the height of the liquid. So, here is how to figure out where to mark your dowel to indicate number of gallons:

Formula to Calculate Height Based on Volume is

h = v/pi r^2

Where h is height, v is volume, pi is 3.1415, and r^2 is radius squared

Note: 1 gallon = 231 cu inches

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Here is an example of how to solve for height in inches of a given volume, in a given pot diameter, say

4 gal. in 14" pot

h = v / (pi)(r^2)

h = 4*231/(3.1415)(7^2)

h = 924/(3.1415)(49)

h = 924/153.93

h = 6" for 4 gallons in 14" pot

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11-12-2011, 03:35 AM   #2
Dilligans
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all I did was pour a gallon of water in a pot then mark it... then poured two gallons then marked it ... 3. 4.. etc... I dont know about using a formula... but then again I forgot everything in learned in high school and college.

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11-12-2011, 03:41 AM   #3
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At first I thought this thread was funny because I thought it was somebody's sarcastic response then I realized it was 100% serious. That formula makes baby Jesus cry.

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Hi

11-12-2011, 03:58 AM   #4
day_trippr
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It better be one hell of a fancy stick...

Cheers

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11-12-2011, 10:31 AM   #5
SwampassJ
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Take the largest accurate measuring cup you have and measure out a gallon in a pitcher or something. Mark the pitcher and then began filling the kettle from the pitcher. Ever addition mark or knotch a spoon or a spare plastic racking tube. The people at the brew store thought it was the neatest thing when I broke out the measuring stick.

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11-12-2011, 10:38 AM   #6
Pappers_
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Quote:
 Originally Posted by Dilligans all I did was pour a gallon of water in a pot then mark it... then poured two gallons then marked it ... 3. 4.. etc... I dont know about using a formula... but then again I forgot everything in learned in high school and college.
This is what I did, too

11-12-2011, 11:32 AM   #7
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Pouring in water is more accurate than measuring and calculating. With every measurement you introduce error. Also pots aren't always perfect cylinders. The error may be minimal, but when you can get it just about perfect with the volume method, why not? There's a time and place for calculation.

Example, you want to figure out the optimal place to put a floor drain. Do you shoot elevations and measure grade to find out where the low point is? No, you spray water on the ground and see where it collects. Easiest answer is usually the best.

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11-12-2011, 11:44 AM   #8
MichaelBrock
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When I first started brewing I set out to take the scientific approach to measuring my volume. The plan was to measure the height of the water with a nice stainless steel ruler and calculate the volume. Unfortunately, my pot has a bowed bottom and that wasn't going to work. So I fell back to pouring water in the pot in set volumes and marking a piece of pvc. The math is pretty but not always practical (and this from a physics degree carrying computer programmer).

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11-12-2011, 11:45 AM   #9
emjay
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GL using this formula in a Blichmann kettle...

Then again, it already has a calibrated sightglass, so I guess it doesn't matter.

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11-12-2011, 12:17 PM   #10
chezhed
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There's a time for common sense/practicality and a time for science.
The smart individual knows when to use what, no matter which

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