How to figure out...

I was listening to a podcast, where someone was able to use a yardstick and multiply the result by some number to get the gallons of wort in his kettle. Since the kettle dimension are different for everyones kettle, does anyone know how to figure this out?
Thanks in advance.

1 gal = .13 cubic feet. So pie r square times decimal feet for the depth. Or you could just pour in a gallon and mark it and repeat.

What I do is mark my yardstick with gallon and half-gallon lines on the back.

I used math to figure out how many inches per gallon, and worked from there.

The volume of a cynlinder is the height times Pi * R^2, where R is the radius.
The only thing I had to look up was the conversion from cubic inches to gallons.

This is kind of a cool idea, I think I might run these calculations and try this.

If you consider your kettle to be a simple cylinder, the volume of the liquid in the kettle would be:
<b> </b>where "r" is the inside radius of the kettle and h is the height of the liquid in it.

If you use a yardstick, this will give you a volume in cubic inches, which you can convert to gallons with the rule:

1 gallon = 231 cubic inches

I took the cheater method and filled my kettle with a 4 gallons of water, stuck my Big Spoon in it, and marked the waver level on the spoon.

Added another 1 gallon of water and made another mark.

Repeat until you have a spoon that can serve as a dip-stick and tell you how much is in the kettle.

If you know you have a 10 gallon kettle, divide the height by 10 to find how many gallons per inch/centimeter. That way, you can measure from the top and still know. I'm all for the calculations, but this may be an easier way. My 15 gallon kettle is 15" tall, so I just know that each inch is 1 gallon.

Edit: I had the numbers backwards. They should be right now.

My keggle has a curved bottom. I poured in gallons of water to find out how many inches per gallon. It came out to:

2.25 inches for the first gallon
1.38 inches for every gallon thereafter....

Therefore, 6 gallons would be 2.25+1.38*5 inches.

Yeah I do the old marked stick for my measurements. I try to limit as much math as possible during my brewday to allow for more fun (ie beer).

I've been meaning to do this for a while now. Somehow it never seems to get done.

can't do this with a Coors keg its not a straight cylinder I had to use the old add a gallon to the HLT and mark the site glass . The keggle was easy its pretty much linear .