I also use the 8 at a time method. The math is easy and you don't end up with bias edges. For whatever unfinished size you want, double that and add one inch. So if I'm needing 3-1/2" unfinished (3" finished), I start with an 8" square. (3.5 + 3.5=7 + 1 = 8") It's a wonderful method and I rarely have to trim.