If you wanted to get a fairly "exact" 6 inch finished block - you could draw out the block on graph paper -
and then make templates from your drawing.
You would only need three templates - one for the squares, one for the side triangles, and one for the corner triangles.
How I make templates:
1) Draw out the "finished" quilt block on graph paper
2) Cut the pieces apart
3) Glue (I used rubber cement) the needed pieces on template plastic, leaving about 3/4 inch between the pieces
4) Add 1/4 inch around the pieces
5) Cut out the templates