This is for you "Techie" types who have a boiling pot or box with no markings on it that tell you how much water it holds. Smaller pots usually have the quart capacity stamped on them.

We're working with cubic inches here. A cubic inch is a square that is 1" X 1" X 1" in size.

Here is how to calculate the round pot.

Equation: Pi (3.14) times the radius (diameter divided by 2) squared (times itself), times the depth of the pot in inches divided by 231 (231 cubic inches in a gallon of fluid (which includes water)).

Example:

I have a pot that is 18" in diameter (measure across the top side to side) and 16" deep. These are rough measurements to the inch.

Pi = 3.14
The radius is 9" (18" divided by two)
The radius squared is 9" X 9" which equals 81.
So now we have 3.14 X 81 X 16 = 4,069 (this is the total cubic inches in the pot)

4,069 / 231 = 17.6 (the number of gallons the pot will hold)

Now, what about a box? 

Simple, forget Pi.

Width X Length X Depth (all in inches)  / 231.

Why would you want to know this seemingly useless information?

Suppose you are going to borrow a big boiler set and want to use my Boiled Crawfish (or Crab) recipe. First thing you want to be able to at least estimate is how much water you're dealing with right?

Now you have the way to do it!