So I finally got a little time to work on my smoker yesterday evening. I was hoping to get my firebox put together and weld in the convection plate. I had just picked up the plates to build my firebox and the first thing I did was cut out the firebox to cooking chamber opening on one of the side plates. As luck would have it, just as I started to make the first weld I hit the end of the spool on my mig. Dang-it!!! Well what seemed like a minor inconvenience at the time may have been a blessing in disguise. So I pick up some mig wire on the way home this afternoon and as I'm getting ready to start working something about that opening just keeps bugging me. No matter how I look at it I just can't see it being anywhere near big enough. Well it seems I have miscalculated the size of that opening. I followed the RF calculator spreadsheet to a "T " except for one minor thing...... the calculator only gives you square, rectangular or round sizes and I needed a semi-circle. I'm no math whiz so I calculated the size in rectangle format which was 3.25 x 4.00. I then took the perimeter of that rectangle and reshaped it into a semi-circle and that's how I figured out how wide my convection plate needed to be (roughly 6.5"). It didn't occur to me at the time that just because the perimeter of a rectangle and a semi-circle are exactly the same doesn't make the interior areas the same. So now I'm left scratching my head. Obviously I'm gonna need a wider convection plate but I don't have a clue how to figure it out. According to the calculator the opening needs to be 12.97 square inches. The interior diameter of my smoke chamber is 11.875". Can someone help me figure out how wide my plate needs to be or point me to some sort of calculator to help me figure surface area of a partial circle.