Figuring out the Firebox Question

[coachin&smokin]

Using the calculator how could I measure this half circle firebox to check to make sure it's 1/3 the size and to see if I have enough air inlets in the box.  Any help is appreciated?  Looking at it I don't think the three squares on the door are enough.  The smoker is 250 gallon tank. 

 

[solaryellow]

The pit building calculator will give you the volume your firebox should be for the size of your cooking chamber. You can then use this ellipsis calculator to help determine the volume of your current firebox and compare the two. http://www.1728.org/ellipse.htm

 

[fourthwind]

or just use the calculator as if it were a complete piece of pipe and then divide by two!  I agree the inlet does not look large enough.  If you are below 4000 feet, I would go with 1.5 time the area of the exhaust pipe.   area of the exhaust is calculated by Radius x 2 x 3.14