I have got a ton of great info on this sight and have been enjoying smoking on my Webber kettle for a few years now. I do not post much but really try to research. I have made some great food and have been proud of my last two briskets. The first two were leather. I could not of figured them out without the posts on here. So let me say thanks for that. I started to build a 120 gal smoker in July but it is bigger than what I need right now and more work than what I can commit to. I have a 20gal that would work perfect for my needs and I should be able to get it done much quicker. Once I figure this one out I will finish the bigger unit. This is the info from the calculator. Link to BBQ Pit Calculator I need help understanding the Firebox to cooker number. It is giving a 6.41 for half moon. When I looked at the tank which is 14in round a 6.41 in wide cut would only be a inch or so off the bottom. I was planning on cutting a 10in wide moon/slot into the tank 3in deep. This would take me through the rounded section of the tank to here it turns flat, stops curving in. It would make the Reverse Flow plate around 2.25 in off the bottom of the tank and 10in wide. So the moon would be 10in wide and 2.25 high. The tank is a estimate 14 inches round and 31inches wide. The straight section is 25 with about 3 inches on each side that rounds to the tip. Thanks for any help or info you can all give. Here is a picture of the tank. Edit: something keeps telling me the plate should be 1/3 of the height of the tank. So if the tank is 14 in high the plate should be 4.5 in off the bottom. Is this correct?