I want to make a quilt that combines square in a square blocks like this one:

http://www.google.com/imgres?imgurl=...Q9QEwBg&dur=62

The small blocks are a square in a square. The larger blocks are a square in a square in a square. If I want my small blocks to finish at 4 inches then the larger block has to finish at 8 inches. I can't figure out the math on the larger square. Can someone with experience give me the dimentions of the inside square, and the squares I would need to make the corners of the 2 "outside squares"?