I'm sure there are several ways, but if I wanted 3" blocks, I would stack my fabric, 3-4 layers, making sure I had a straight edge, I would cut 3" strips. Then I would take each set of strips, and keep cutting the squares at 3". Your length of strips would be determined by how many 3" squares you needed. (or what ever size you need). You would then have squares ready to sew together. Hope I'm making sense.