Are you wanting to know how much material for the 8" block?
I make a 12 1/2" block and use( 5) 6 1/2" squares. 2 of one color and 3 of another. So if you want an 8" finished block, use 4 1/2" squares, 2 of one color and 3 of the other. However, the smaller the squares, the harder it is to do the middle square.
I also tried (4) 6 1/2" squares and the center square was 12 1/2" square. Once you figure out how much material you need for each block, then multply that times the # of blocks you need.