So how hard would it be for big kettle manufacturers to publish a volume/depth chart with purchase of their kettles? I have a nice Polarware 10-gal pot, and I bet it would have been pretty easy for them to provide that info with purchase. Just sayin'.
Which 10-gallon Polar Ware stockpot do you own? Polar Ware offers one made in the U.S.A. 10-gallon stockpot (model 360) and a factory converted version of this stockpot called the Brew Pot (models 361BP and 362BP), one made in the China 10-gallon stockpot called the BrewRite Brew Kettle (model T5140), and one made in China 10-gallon Economy Brew Pot (model T422BPTT). I own the made in U.S.A. 10-gallon Brew Pot (model 360BP). The 361BP is easy to pick out of the line-up because it has factory welded fittings.
The internal dimensions of the 361BP are roughly 14" wide by 16" tall (the Polar Ware specified width of 15" includes the rolled lip at the top of the kettle). The BP361 holds approximately (~) 10.5 gallons when filled to the top.
Here are measurements for the 361BP:
height_of_one_US_gallon = 231 / (3.14 x 72) = ~1.5"
0.375" = ~1/4 gallon
0.75" = ~1/2 gallon
1.5" = ~ 1 gallon
As mentioned above, the volume of a liquid expands by roughly 5% at 100C (212F); hence, one's end of boil measurement should be approximately 1.05 times the volume one wants to achieve after chilling. While not perfectly accurate, multiplying the volume at 100C by 0.95 will give one the approximate volume at room temperature (i.e., the multiplicative inverse of 1.05 = 1 / 1.05 = 0.95238)
I did some careful measurements a few years ago and determined that my kettle is 1.5" height per gallon. And I had read that wort increases in volume by 4% at boiling, so I typically measure preboil wort right after the hot break happens and the foam settles down. I multiply by 0.96 to get my volumes.
The point is - maybe that info was readily accessible to me a few years ago, but it sure didn't come with the kettle.