Im making a window that is 300” I divide it up into 9 equal parts autocad lt 2012 divides it up @ 31 1/8” that is 280 1/8”
The mullions are two inches wide and there is 10 of them that equals 20” the caulk joints are 3/8” there are two of them that equals 3/4"
So 280 1/8” + 20” = 300 1/8” + 3/4 “ = 300 7/8”