Hello I have one of northern brewer discontinue 10gal tall boy kettle. So my question is I am trying to figure out how many inches would equal 1gal so I can make a dip stick with gallons marks on it...See here are the Dimensions: Height: 16.75" without Lid; 18.75" with Lid. Width: 15" at Top of Kettle; 14.5" at Bottom of Kettle; 18.5" Handle to Handle. Inner Diameter: 13.75"...
I did it the other way around.Take a gallon jug,
Fill it with water. Dump it in the kettleMark the dipstick
When I verify my volume markings I measure by weight. If I'm not mistaken I think there is a online calculator that can tell you height per gallon based on kettle dimensions. If I come across it I will post link.
I always do these sort of things the way @jmck says. Here's a great article on etching your kettle.https://byo.com/project/etch-your-kettle-projects/
I etched my Tall Boy kettle this way. It was not totally accurate but close enough. I later added a sight glass on the outside for better accuracy.
I did the exact same thing. Used a piece of CPVC pipe and marked it at 5 gallon increments by scoring it. For a MT anything in between was close enough.