The formula for the sew around the edges according to Ceil is:
size of block you start with minus .5, times 1.4, minus .5 for the unfinished size.
So if you start with 6" blocks it would be:
6 - .5 = 5.5
5.5 x 1.4 = 7.7
7.7 - .5 = 7.2 trim to 7"
Take off seam allowance and it finishes to 6.5".
HTH