How to caculate how much wort is in a kettle

For those who are just beginning to brew, figuring out how much wort is in one's kettle at any point in the boil is a simple mathematical exercise.

We start by calculating volume that the wort displaces in cubic inches. The formula for calculating the volume of wort in a cylinder is:

volume_of_wort_in_square_inches = 3.14 x the_radius_of_our_kettle_in_inches x the_radius_of_our_kettle_in_inches x the_height_of_our_wort_in_inches

For example, if we measure 8" of wort in a stockpot that has a diameter of 14", then the volume of the wort is 3.14 x 7 x 7 x 8 = 1,230 cubic inches.

Next, we have to convert cubic inches to gallons. There are 231 cubic inches in a gallon; therefore, we have 1,230 / 231 = 5.33 gallons of wort in our kettle.

As one can clearly see, one doesn't need a fancy sight gauge or markings on a pot to determine how much wort is in one's kettle. All one needs is a clean metal ruler and a calculator (use a sanitized metal ruler if the wort has already been chilled).

I just mark my spoon at 5, 6 and 7 gallon intervals. I don't need to be doing math on brew day!

masskrug said:

I just mark my spoon at 5, 6 and 7 gallon intervals. I don't need to be doing math on brew day!

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^^^ This. I marked my mash paddle then switched pots so I made a dip stick. I measured out a gallon in a jug with a measuring cup. Filled a gallon, made a mark, added another gallon, made a mark, etc.

masskrug said:

I just mark my spoon at 5, 6 and 7 gallon intervals. I don't need to be doing math on brew day!

Click to expand...

You made my day.. I am rolling on the floor

masskrug said:

I just mark my spoon at 5, 6 and 7 gallon intervals. I don't need to be doing math on brew day!

Click to expand...

That's what I did when I first started to brew. However, I switched over to using cubic inches after I started to brew different lengths of beer in different-sized kettles. I can run several calculations in the time that it takes to fill a kettle and mark a spoon.

EarlyAmateurZymurgist said:

That's what I did when I first started to brew. However, I switched over to using cubic inches after I started to brew different lengths of beer in different-sized kettles. I can run several calculations in the time that it takes to fill a kettle and mark a spoon.

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True, but I always use the same pot so I did the fill and mark routine 1 1/2 years ago. It took about 15 minutes and now I never have to make any calculations. Just dip and look at the marks.

Ye olde spoonometer®. Calibrated with ye olde random "near a gallon" volumetric device.

You could make a plastic or wooden ruler in the shape of a spoon or paddle. You could even mark one side in fractions of an inch and the other in gallon and quart equivalents. Then when you drop your calculator in your wort, you can still brew

The first inch of my pot doesn't have the same volume as the rest of the inches. Anyone else have that problem

Now I need to go calculate how much longer my plastic spoon gets when it's hot. Hmmm. It grows about 10 times as much as a steel ruler which grows about four times as much as a wooden paddle. I guess we'd be better off with a wooden ruler. We could even do the calculations and mark it ahead of time. Wait a minute.

Seriously, this is a good alternate way to initially mark your measuring tool but it seems like unnecessary work to keep doing the math and not creating a direct measuring device. Besides that it allows the introduction of errors every time you have to calculate.

mine is easy. 30 qt pot is 15 inches tall, so 2 qts per inch

& I use an aluminum ruler.

x2 or /2 is not too much math for a brew day

I have ONE mark on my mash paddle that is finished batch size, a 1/4 keg...I eyeball two plus inches above that for pre boil, and an inch or so above that for post boil to account for yeast cake, thermal shrinkage and losses to trub and hop debris.

EarlyAmateurZymurgist said:

However, I switched over to using cubic inches.....

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Wow...measuring your brewing volumes to the 1/2 ounce.

This thread reminds me of the missing strawberries on the USS Caine...
Part 1 https://www.youtube.com/watch?v=1EO_8dDKTsU
Part 2 https://www.youtube.com/watch?v=U8LR2okL8YM

Have fun with a keg. You'll need to approximate a function for the sloping side walls and integrate the volume based on the height.

Um, yeah I'm a nerd, but not after a few beers. Sight glass, thank you very much.

Mine is nice, 1 inch=1 gallon