Well I make it 2(11+6*2+5)+6+6cm
Can you see where the numbers come from?
2(11+6*2+5)+6+6 cm = 2(A+B*2+D)+C+C cm (Please see attached edited diagram)
2(A+B*2+D) - This part deals with the rectangles at the top and bottom. It is multiplied by two as they are the same.
+C+C cm - This part deals with the square in the middle.
As the image is equal round the center axis you could change it to:
2(11+6*2+11) cm which should give you the same answer, but as I have not had my coffee yet I would not guarantee it!